Electrochemical and electronic devices

Abstract

To provide an electrochemical device and an electronic device that improve the rate characteristics of the electrochemical device under low and normal temperatures.SOLUTION: An electrochemical device includes a positive electrode piece, the positive electrode piece includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material. In a scanning electron micrograph of a cross section of the positive electrode material layer, when the radius of the smallest circumscribing circle of the contour of positive electrode active material particles having an area of more than 5 μm2 is represented by Rc and the radius of the largest inscribing circle of the contour of the positive electrode active material particles having an area of more than 5 μm2 is represented by Ri, Rc and Ri satisfy 1<average value of Rc / Ri≤3. In the electrochemical device, when the positive electrode active material in the positive electrode material layer satisfies 1<average value of Rc / Ri≤3, the transport efficiency of lithium ions can be effectively improved, and the rate characteristics of the electrochemical device under room temperature and low temperature can be improved.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of electrochemistry, and in particular to electrochemical and electronic devices. [Background technology]

[0002] Due to advantages such as high energy density, long cycle life, and no memory effect, lithium-ion batteries are widely used in fields such as wearable devices, smartphones, drones, electric vehicles, and large-scale energy storage devices, and are currently the new green chemical power source with the most promising development prospects worldwide. As lithium-ion batteries are widely applied, the market demands further improvement in the overall performance of lithium-ion batteries.

[0003] The positive electrode active material, negative electrode active material, and electrolyte in a lithium-ion battery are important parameters that affect the performance of the lithium-ion battery. The selection of the positive electrode active material affects the lithium ion transport efficiency, thereby affecting the electrochemical performance, such as the rate capability, of the electrochemical device. However, conventional positive electrode active materials need to be further optimized to improve the rate capability of the electrochemical device. Summary of the Invention

[0004] An object of the present invention is to provide an electrochemical device and an electronic device that improve the rate characteristics of the electrochemical device at low and normal temperatures.

[0005] A first aspect of the present invention is an electrochemical device including a positive electrode piece, the positive electrode piece including a positive electrode material layer, the positive electrode material layer including a positive electrode active material, and a scanning electron microscope photograph of a cross section of the positive electrode material layer showing an area of ​​5 μm 2 The radius of the smallest circumscribed circle of the positive electrode active material particle is R. c and the area is 5 μm 2 The radius of the maximum inscribed circle of the contour of the positive electrode active material particle is R. i When R c and R i is 1 <Rc / R i For example, an electrochemical device is provided in which the average value of R c / R i The average value of may be 1.1, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, or may be in a range consisting of any two of these values. Without being limited by any theory, in the electrochemical device provided by the present invention, it is believed that the positive electrode active material in the positive electrode material layer is 1 <R c / R i By satisfying the average value of R≦3, the transport efficiency of lithium ions during the charge and discharge process can be effectively improved, thereby improving the rate characteristics of the electrochemical device at room temperature and low temperature (for example, below 0°C). c / R i It is believed that the reason for this is that the morphology of the positive electrode material layer in which the average value of (a) is within the above range allows the positive electrode active material to maintain a stable crystal structure during high-rate cycling, effectively improves the lithium ion absorption and desorption dynamics of the positive electrode active material, and provides good lithium ion transport properties, thereby improving the rate performance of the electrochemical device. In the present invention, the cross section of the positive electrode material layer refers to a cross section obtained by cutting the positive electrode material layer laterally along the thickness direction.

[0006] In some embodiments of the present invention, the area is 5 μm 2 The positive electrode active material particles include a first particle and a second particle, and the radius of the smallest circumscribing circle of the outline of the first particle is R c1 The radius of the maximum inscribed circle of the contour of the first particle is R i1 When R c1 and R i1 is 1 <R c1 / R i1 The average value of ≦1.5 is satisfied, and the radius of the smallest circumscribing circle of the outline of the second particle is R c2 The radius of the maximum inscribed circle of the contour of the second particle is R i2 When R c2 and R i2 is 1.5 <R c2 / R i2 The average value of is ≦3.

[0007] With respect to the cross-sectional area of ​​the positive electrode material layer, the area percentage of the first particles is more than 0% and 50% or less, and the area percentage B of the second particles is 30% to 80%. c1 / R i1 The average value of R may be 1.1, 1.2, 1.3, 1.4, 1.5, or a range consisting of any two of these values. c2 / R i2 The average value of may be 1.6, 2, 2.5, 3, or may be in a range consisting of any two of these values. The area percentage of the first particles may be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or may be in a range consisting of any two of these values. The area percentage B of the second particles may be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or may be in a range consisting of any two of these values.

[0008] The first particles and the second particles are distributed in the positive electrode material layer in the above ratio, and after the compression process, the positive electrode material layer is c / R i This achieves an interwoven distribution between particles of different sizes and improves the distribution network of the positive electrode active material and conductive agent, effectively reducing side reactions at the interface within the positive electrode layer, improving lithium ion transport efficiency and electrical conductivity within the positive electrode pieces, and effectively improving the rate and cycle characteristics of the electrochemical device. If the area percentage B of the second particles is too small (e.g., less than 30%), the area percentage of the first particles is too large, reducing the compaction density of the positive electrode pieces and affecting the lithium ion transport efficiency. If the area percentage B of the second particles is too large (e.g., greater than 80%), this similarly reduces the compaction density of the positive electrode pieces, affecting the lithium ion transport efficiency and thereby affecting the rate characteristics of the electrochemical device at room and low temperatures. Adjusting the area percentages of the first particles and the second particles within the ranges of the present invention is advantageous for improving the rate characteristics of the electrochemical device at room and low temperatures. In the present invention, the compaction density of the positive electrode pieces refers to the compaction density of the positive electrode material layer in the positive electrode pieces.

[0009] In some embodiments of the present invention, the average cross-sectional area of ​​the first particles is smaller than the average cross-sectional area of ​​the second particles, which is advantageous for reducing lithium ion transport pathways and improving the rate characteristics of the electrochemical device.

[0010] In some embodiments of the present invention, the electrochemical device satisfies at least one of the conditions (a) to (b). (a) The positive electrode active material includes lithium manganate, and the lithium manganate includes doped lithium manganate and / or lithium manganate containing a coating layer. In the present invention, the doping element in the doped lithium manganate is not particularly limited as long as the object of the present invention can be achieved. For example, the doping element may include at least one of Al, Nb, Mg, Ti, F, B, Zr, W, Sr, Y, Ce, and La, but is not limited thereto. In the present invention, the element in the coating layer in the lithium manganate containing a coating layer is not particularly limited as long as the object of the present invention can be achieved. For example, the element in the coating layer may include at least one of Al, Sr, Zr, Ti, and B, but is not limited thereto. (b) The positive electrode active material includes a composite metal oxide of lithium and a transition metal element, the transition metal element including Mn and a metal element M1, the metal element M1 including at least one of Ni, Co, and Fe. With respect to the mass of the positive electrode active material, the mass fraction of Mn is 30% to 65%, and the mass fraction of the metal element M1 is 2% to 25%. When the electrochemical device satisfies at least one of the conditions (a) and (b), it is advantageous for improving the cycle characteristics and low-temperature rate characteristics of the electrochemical device.

[0011] In some embodiments of the present invention, the second particles include a metal element M2, and the metal element M2 includes at least one of Al, Mg, and Nb.

[0012] In some embodiments of the present invention, the mass fraction of the metal element M2 is 0.1% to 3% relative to the mass of the second particles, for example, the mass fraction of the metal element M2 may be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3%, or a range consisting of any two of these values.

[0013] In the related art, manganese-containing positive electrode active materials (e.g., lithium manganate) are widely applied in electrochemical devices, such as lithium-ion batteries. However, the Mn present in lithium manganate 3+ is prone to disproportionation reactions, so manganese (Mn 2+ This causes the dissolution of lithium ions, which then migrate through the electrolyte to the negative electrode and destroy the solid electrolyte interface (SEI) film of the negative electrode. However, in order to repair the SEI film, active lithium is lost, thereby affecting the cycle characteristics and rate characteristics of the lithium ion battery. In the present invention, the negative electrode may also refer to a negative electrode piece.

[0014] The inventors of the present invention have found that, for an electrochemical device including a manganese-containing positive electrode active material, when the positive electrode active material contains a metal element M1, selecting the above metal element M1 is advantageous in improving the manganese elution phenomenon, thereby reducing damage to the negative electrode SEI film and loss of active lithium due to consumption of lithium to repair the SEI film, thereby improving the cycle characteristics and rate characteristics of the electrochemical device.

[0015] The inventors of the present invention have found that when the second particles contain a metal element M2, selecting the above metal element M2 can reduce the interfacial side reaction between the second particles and the electrolyte during low-temperature charging and discharging, thereby improving the internal resistance of the positive electrode pieces and enhancing the low-temperature rate characteristics of the electrochemical device.

[0016] The inventors of the present invention found that if the mass fraction of the metal element M2 is too low (e.g., less than 0.1%), the side reaction between the second particles and the electrolyte is not significantly improved. They also found that if the mass fraction of the metal element M2 is too high (e.g., greater than 3%), the side reaction between the second particles and the electrolyte cannot be further improved, and the capacity per gram of the positive electrode active material decreases. They also found that adjusting the mass fraction of the metal element M2 within the above range is advantageous for reducing the interfacial side reaction between the second particles and the electrolyte and improving the cycle characteristics of the electrochemical device. In the present invention, the term "negative electrode" may refer to a negative electrode piece.

[0017] In some embodiments of the present invention, the volumetric particle size distribution of the positive electrode active material satisfies at least one of the following conditions: (c) 9 μm≦Dv50≦22 μm; and (d) 0.9≦(Dv90−Dv10) / Dv50≦2. For example, the Dv50 of the positive electrode active material may be 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, or 22 μm, or may be within a range consisting of any two of these values. For example, the value of (Dv90−Dv10) / Dv50 may be 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2, or may be within a range consisting of any two of these values. Adjusting the volumetric particle size distribution of the positive electrode active material to satisfy at least one of conditions (c) and (d) is advantageous in improving the rate characteristics of the electrochemical device at room temperature and low temperatures. In the present invention, the Dv90 and Dv10 of the positive electrode active material are not particularly limited as long as the value of (Dv90-Dv10) / Dv50 is within the above range. For example, the Dv90 of the positive electrode active material is 15 μm to 40 μm, and the Dv10 of the positive electrode active material is 0.5 μm to 6 μm. Here, the value of (Dv90-Dv10) / Dv50 mainly reflects the particle size distribution of the positive electrode active material.

[0018] In some embodiments of the present invention, the electrochemical device further includes an electrolyte containing a chain carbonate ester and a cyclic carbonate ester. When the mass fraction of the chain carbonate ester, ω1, and the mass fraction of the cyclic carbonate ester, ω2, are defined as 25% to 50% relative to the mass of the electrolyte, respectively, ω2 is 25% to 50%, and ω1 / ω2 is 0.75 to 2.5. For example, the mass fraction of the cyclic carbonate ester, ω2, may be 25%, 30%, 35%, 40%, 45%, or 50%, or may be within a range consisting of any two of these values. The value of ω1 / ω2 may be 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, or 2.5, or may be within a range consisting of any two of these values.

[0019] Without being limited by any theory, the R c / R i By adjusting the average value and including a chain carbonate ester and a cyclic carbonate ester in the electrolyte, a synergistic effect occurs between the positive electrode active material and the electrolyte, making it possible to improve the lithium ion transport path, particularly the lithium ion transport efficiency at the interface between the positive electrode active material and the electrolyte, thereby improving the rate characteristics of the electrochemical device.

[0020] Without being limited by any theory, if the mass fraction ω2 of the cyclic carbonate is too low (e.g., less than 25%), a good synergistic effect between the cyclic carbonate and the chain carbonate cannot be formed to improve lithium ion transport efficiency. If the mass fraction ω2 of the cyclic carbonate is too high (e.g., greater than 50%), the viscosity of the electrolyte increases, which is unfavorable for lithium ion transport and thereby affects the rate performance of the electrochemical device. If the ω1 / ω2 value is less than 0.75 or greater than 2.5, the synergistic effect between the cyclic carbonate and the chain carbonate is affected, thereby affecting the lithium ion transport efficiency. By adjusting the mass fraction ω2 of the cyclic carbonate and the ω1 / ω2 values ​​within the ranges of the present invention, the positive electrode active material can be sufficiently infiltrated, thereby improving the lithium ion transport efficiency at the interface between the positive electrode active material and the electrolyte and further improving the rate performance of the electrochemical device.

[0021] In some embodiments of the present invention, ω1 satisfies the range 35%≦ω1≦65%. For example, the mass fraction ω1 of the chain carbonate ester may be 35%, 40%, 45%, 50%, 55%, 60%, or 65%, or may be within a range consisting of any two of these values. Without being limited by any theory, adjusting the mass fraction ω1 of the chain carbonate ester within the range of the present invention is advantageous for forming a good synergistic effect between the cyclic carbonate ester and the chain carbonate ester, improving the transport efficiency of lithium ions and thereby improving the rate characteristics of the electrochemical device.

[0022] In some embodiments of the present invention, the chain carbonate ester includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), methyl isopropyl carbonate, methyl butyl carbonate, and dibutyl carbonate (DBC). Without being limited by theory, selecting the above chain carbonate ester is advantageous for improving lithium ion transport efficiency and improving the rate characteristics of the electrochemical device.

[0023] In some embodiments of the present invention, the cyclic carbonate ester includes at least one of ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Without being limited by any theory, the selection of the above cyclic carbonate ester is advantageous in improving the transport efficiency of lithium ions and the rate characteristics of the electrochemical device.

[0024] In some embodiments of the present invention, the electrolyte solution contains a sulfonate ester compound, and A satisfies the relationship 0.006≦A / B≦0.1, where A is the mass fraction of the sulfonate ester compound relative to the mass of the electrolyte solution. For example, the value of A / B may be 0.006, 0.008, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, or a range consisting of any two of these values. Without being limited by theory, the sulfur-oxygen double bond in the sulfonate ester compound is beneficial for improving the stability of the SEI film and reducing the deposition of leached manganese on the negative electrode, thereby improving the cycle performance of the electrochemical device. At the same time, when the value of A / B is within the range of the present invention, a synergistic effect between the sulfonate ester compound and the positive electrode active material is favored, which improves the stability of the SEI film, improves lithium ion transport efficiency, and further improves the rate performance of the electrochemical device.

[0025] In some embodiments of the present invention, A satisfies the range of 0.5%≦A≦10%. For example, the mass fraction A of the sulfonate ester compound may be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or may be in a range consisting of any two of these values. Without being limited by any theory, if the mass fraction A of the sulfonate ester compound is too low (e.g., less than 0.5%), no significant improvement in the stability of the SEI film is observed. If the mass fraction A of the sulfonate ester compound is too high (e.g., more than 10%), an SEI film that is too thick or too dense is formed, which inhibits lithium ion transport and reduces the rate capability of the electrochemical device.

[0026] Preferably, the sulfonate ester compound includes at least one of compounds I-1 to I-14 having the following structures: Selecting a sulfonate ester compound having the following structure is advantageous for improving the stability of the SEI film and reducing the deposition of eluted manganese on the negative electrode, thereby improving the cycle characteristics of the electrochemical device. [ka]

[0027] In some embodiments of the present invention, the electrochemical device further includes a negative electrode sheet, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, and hard carbon. Without being limited to any theory, by selecting the above negative electrode active material, it is advantageous to form a synergistic effect between the positive electrode active material and / or the electrolyte, and improve the cycle characteristics and rate characteristics of the electrochemical device.

[0028] In the present invention, the positive electrode active material may include, but is not limited to, a composite oxide, and at least one of a sulfide, a selenide, and a halide of the composite oxide. The composite oxide may include, but is not limited to, LiMn2O4, Li(Ni a1 Co b1 Mn c1 )O2 (0 < a1 < 1, 0 < b1 < 1, 0 < c1 < 1, a1 + b1 + c1 = 1), LiNi 1-y1 Co y1 O2 (0 < y1 < 1), LiNi 2-y3 Mn y3 O4 (0 < y3 < 2), Li(Ni a3 Co b3 Al c3 )O2 (0 < a3 < 1, 0 < b3 < 1, 0 < c3 < 1, a3 + b3 + c3 = 1), and LiMn p Fe q PO4 (0 < p < 1, 0 < q < 1, p + q = 1), and at least one of LiFePO4, but is not limited thereto.

[0029] Optionally, an amorphous compound or a crystalline compound may be present on the surface of the composite oxide, and the amorphous or crystalline compound may include, but is not limited to, at least one of an oxide of element Z, a hydroxide of element Z, an oxyhydroxide of element Z, an oxycarbonate of element Z, and a basic carbonate of element Z. Here, element Z may include, but is not limited to, at least one of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, and Zr.

[0030] ​In the present invention, the method for preparing the composite oxide containing an amorphous compound or a crystalline compound on the surface is not particularly limited as long as the object of the present invention can be achieved, and examples thereof include the spray method and the deep method.

[0031] In the present invention, the positive electrode material layer may further contain a conductive agent. In the present invention, the conductive agent is not particularly limited as long as the object of the present invention can be achieved. For example, the conductive agent may include at least one of conductive carbon black (SuperP), carbon nanotubes (CNTs), carbon fiber, Ketjen black, graphene, metal materials, and conductive polymers, but is not limited thereto. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and multi-walled carbon nanotubes. The carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanocarbon fiber. The metal material may include, but is not limited to, metal powder and metal fiber. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and platinum. The conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, and polypyrrole. In the present invention, the mass fraction of the conductive agent relative to the mass of the positive electrode material layer is 0.5% to 5%.

[0032] In the present invention, the positive electrode material layer may include a positive electrode binder. In the present invention, the positive electrode binder is not particularly limited as long as the object of the present invention can be achieved, and examples thereof include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethyleneoxy-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated (esterified) styrene-butadiene rubber, epoxy resin, and nylon, but is not limited to these.

[0033] In the present invention, the positive electrode piece includes a positive electrode current collector. Here, the positive electrode current collector is not particularly limited as long as the object of the present invention can be realized, and may include, for example, aluminum foil, aluminum alloy foil, and composite current collector, but is not limited thereto. In the present invention, the thickness of the positive electrode current collector is not particularly limited as long as the object of the present invention can be realized, and for example, the thickness is 8 μm to 20 μm.

[0034] Optionally, the positive electrode piece may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. In the present invention, the composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the art, for example, it may include the above-mentioned conductive agent and the above-mentioned positive electrode binder, but is not limited thereto.

[0035] In the present invention, the negative electrode material layer may contain a conductive agent. In the present invention, the conductive agent is not particularly limited as long as the object of the present invention can be realized, and may contain, for example, at least one of the above-mentioned conductive agents, but is not limited thereto.

[0036] In the present invention, the negative electrode material layer may further include a negative electrode binder. In the present invention, the negative electrode binder is not particularly limited as long as the object of the present invention can be achieved, and may include, for example, at least one of difluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethyleneoxy, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated (esterified) styrene-butadiene rubber, epoxy resin, and nylon, but is not limited to these.

[0037] In the present invention, the negative electrode piece includes a negative electrode current collector. Here, the negative electrode current collector is not particularly limited as long as the object of the present invention can be achieved, and may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and composite current collectors. In the present invention, the thickness of the negative electrode current collector is not particularly limited as long as the object of the present invention can be achieved, and for example, the thickness is 4 μm to 12 μm.

[0038] Optionally, the negative electrode piece may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. In the present invention, the composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in the art, and the conductive layer may include, but is not limited to, the above-mentioned conductive agent and the above-mentioned negative electrode binder.

[0039] In the present invention, the electrolyte solution may further contain a non-aqueous solvent. In the present invention, the non-aqueous solvent is not particularly limited as long as the object of the present invention can be realized, and may include, for example, at least one of a carboxylic acid ester compound, an ether compound, and other organic solvents, but is not limited thereto. Examples of the carboxylic acid ester compound include methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, 2,2-difluoroethyl acetate, valerolactone, butyrolactone, 2-fluoroethyl acetate, 2,2-difluoroethyl acetate, ethyl trifluoroethyl acetate, 2,2,3,3,3-pentafluoropropionate, 2,2 ,3,3,4,4,4,4-heptafluorobutyrate, methyl 4,4,4-trifluoro-3-(trifluoromethyl)butyrate, 2,2,3,3,4,4,5,5,5,5-nonafluorovalerate, methyl 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononanoate, and ethyl 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononanoate. The ether compounds may include, but are not limited to, at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and bis(2,2,2-trifluoroethyl)ether. The other organic solvents may include, but are not limited to, at least one of ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0040] In the present invention, the electrolyte may further contain a lithium salt. In the present invention, the lithium salt is not particularly limited as long as the object of the present invention can be realized, and examples thereof include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium bis(oxalato)borate (LiB(C2O4)2), lithium difluorooxalatoborate (LiBF2(C2O4)), lithium hexafluoroantimonate (LiSbF6), lithium perfluorobutylsulfonate (LiC4F9SO3), lithium perchlorate (LiClO4), lithium aluminate (LiAlO2), lithium tetrachloroaluminate (LiAlCl4), lithium bissulfonimide (LiN(C x F 2x+1 SO2)(C y F 2y+1 The lithium salt may include at least one of lithium fluoride (LiF), but is not limited to these. Preferably, the lithium salt includes LiPF. In the present invention, the concentration of the lithium salt is not particularly limited as long as the object of the present invention can be achieved, and the concentration is, for example, 0.5 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L, and more preferably 0.6 mol / L to 1.5 mol / L.

[0041] The electrochemical device of the present invention further includes a separator. In the present invention, the separator is not particularly limited as long as the object of the present invention can be achieved. For example, the separator may include at least one of polyethylene (PE), polypropylene (PP), polytetrafluoroethylene-based polyolefin (PO) separators, polyester films (e.g., polyethylene terephthalate (PET) film), cellulose films, polyimide films (PI), polyamide films (PA), spandex or aramid films, woven films, nonwoven films, microporous films, composite films, separator sheets, pressed films, and spun films, but is not limited thereto. The separator of the present invention may have a porous structure, and the pore size is not particularly limited as long as the object of the present invention can be achieved. For example, the pore size may be 0.01 μm to 1 μm. In the present invention, the thickness of the separator is not particularly limited as long as the object of the present invention can be achieved. For example, the thickness may be 5 μm to 500 μm.

[0042] For example, the separator may include a separator substrate layer and a surface treatment layer. The separator substrate layer may be a nonwoven fabric, membrane, or composite membrane having a porous structure, and the material of the separator substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, etc., but is not limited to these. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the separator substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.

[0043] The polymer layer may include, but is not limited to, at least one of vinylidene fluoride, vinylidene fluoride-hexafluoropropyl copolymer, polyacrylonitrile, polyimide, acrylonitrile-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, acrylic acid-styrene copolymer, polydimethylsiloxane, sodium polyacrylate, and carboxymethyl cellulose. The inorganic layer may include, but is not limited to, inorganic particles and an inorganic binder. In the present invention, the inorganic particles are not particularly limited and may include, but are not limited to, at least one of ceramic, aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In the present invention, the inorganic layer binder is not particularly limited, and may include, for example, at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene, but is not limited thereto.

[0044] The electrochemical device of the present invention is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0045] The process for preparing an electrochemical device is well known to those skilled in the art and is not particularly limited in the present invention. For example, the process may include, but is not limited to, the following steps: Positive electrode pieces, separators, and negative electrode pieces are stacked in order, and the stack is wound, folded, or otherwise processed as necessary to obtain a wound electrode assembly. The electrode assembly is then placed in a packaging bag, an electrolyte is poured into the packaging bag, and the bag is sealed to obtain an electrochemical device. Alternatively, positive electrode pieces, separators, and negative electrode pieces are stacked in order, and the four corners of the entire stack are secured with tape to obtain a stacked electrode assembly. The electrode assembly is then placed in a packaging bag, an electrolyte is poured into the packaging bag, and the bag is sealed to obtain an electrochemical device. Furthermore, an overcurrent protection element, lead plates, etc. may be provided in the packaging bag as needed to prevent internal pressure buildup and overcharging and discharging of the electrochemical device.

[0046] A second aspect of the present invention provides an electronic device comprising an electrochemical device according to any of the embodiments of the present invention. The electrochemical device provided by the present invention has good rate and cycle characteristics, thereby allowing the electronic device provided by the present invention to have a long service life.

[0047] The electrochemical device of the present invention is not particularly limited and may be used in any electronic device known in the prior art. In some embodiments, the electronic device of the present invention may include, but is not limited to, notebook computers, pen-based 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, minidiscs, walkie-talkies, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium ion capacitors.

[0048] The present invention provides an electrochemical device including a positive electrode piece, the positive electrode piece including a positive electrode material layer, the positive electrode material layer including a positive electrode active material, and a scanning electron micrograph of a cross section of the positive electrode material layer showing a cross-sectional area of ​​5 μm 2 The radius of the smallest circumscribed circle of the positive electrode active material particle is R. c The cross-sectional area is 5 μm 2 The radius of the maximum inscribed circle of the particle contour is R. i When R c and R i is 1 <R c / R i In the electrochemical device provided by the present invention, the positive electrode active material in the positive electrode material layer satisfies the average value of ≦3. <R c / R i By satisfying the average value≦3, the transport efficiency of lithium ions in the positive electrode pieces can be effectively improved, thereby improving the rate characteristics of the electrochemical device at room temperature and low temperature. [Brief explanation of the drawings]

[0049] In order to more clearly explain the embodiments of the present invention and the technical solutions of the prior art, the following will briefly describe the drawings used in the embodiments and the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. [Figure 1] FIG. 1 is a scanning electron microscope photograph of a cross section of a positive electrode material layer in one embodiment of the present invention. [Figure 2] 2 is a cross-sectional view of a positive electrode piece according to one embodiment of the present invention, in which reference numerals refer to: 10, positive electrode current collector; 20, positive electrode material layer; 21, positive electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0050] In order to clearly illustrate the objectives, technical solutions and advantages of the present invention, the present invention will be described in more detail below with reference to the drawings and examples. Obviously, the described examples are only some of the embodiments of the present invention, and do not cover all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention fall within the scope of protection of the present invention.

[0051] 1 shows a scanning electron microscope photograph of a cross section of a positive electrode material layer in one embodiment of the present invention. As can be seen from the drawing, there are differences in the size and shape of the particles of the positive electrode active material 21. The smallest circumscribing circle of the outline of particle C is R1, the largest inscribing circle of the outline of particle C is R2, the smallest circumscribing circle of the outline of particle D is R3, and the largest inscribing circle of the outline of particle D is R4. Here, particle C is an example of a first particle in the present invention, and particle D is an example of a second particle in the present invention.

[0052] FIG. 2 is a schematic cross-sectional view of a positive electrode piece in one embodiment of the present invention, in which a positive electrode material layer 20 is present on both surfaces of a positive electrode current collector 10, and the direction indicated by the arrow in the figure is the thickness direction of the positive electrode material layer 20. The cross section of the positive electrode material layer described in the present invention refers to a cross section obtained by crossing along the direction of the arrow in the figure.

[0053] In the embodiment of the present invention, the R c1 / R i1 and the average value of the second particle R c2 / R i2 The average value of can be controlled by controlling the ratio of the radius of the smallest circumscribing circle to the radius of the largest inscribing circle of the outline of the raw material particles, and the Dv50 of the raw material, and by comprehensively adjusting conditions such as the stirring speed or firing temperature during the preparation process of the positive electrode active material.

[0054] In the embodiments of the present invention, the present invention will be described using a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present invention is not limited to a lithium ion battery.

[0055] Example Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out as follows. Unless otherwise specified, "parts" and "%" are by mass.

[0056] Measurement methods and devices: R i and Rc Measurement of: At 25°C, the lithium-ion battery was charged to 4.2 V at a constant current of 0.5 C, then further charged at 4.2 V at a constant voltage of 0.05 C, and discharged to 2.8 V at a constant current of 1 C. The lithium-ion battery was disassembled, and the positive electrode pieces were washed with DMC and dried at 60°C for 2 hours. The positive electrode pieces were then cut along their thickness using an ion polisher to obtain flat cross sections. The cross sections were measured using a scanning electron microscope (SEM), and SEM images at a magnification of 1000x were selected.

[0057] ImageJ software was used to perform shape recognition on the above SEM image, and the cross section was determined to be completely within the image field and with a cross-sectional area of ​​5 μm 2 Randomly select 100 particles, and use the algorithm to calculate the radius of the maximum inscribed circle of the particle, R i and the radius of the minimum circumscribed circle R c were calculated (see "Kenneth C. Williams, Wei Chen, Sebastian Weeger, Timothy J. Donohue, Particle shape characterization and its application to discrete element modeling, Particuology, Volume 12, 2014, Pages 80-89, ISSN 1674-2001").

[0058] R c1 , R i1 , R c2 , R i2 The measurement method is R i and R c It was the same as

[0059] R c3 and R i3 The measurement of R was carried out by first preparing manganese dioxide into a slurry, coating it on a substrate to form a film layer, and then measuring the R i and R cThe solid content of the slurry (e.g., 75 wt%) and the type of the substrate are not particularly limited as long as the object of the present invention can be achieved. c4 and R i4 , R c5 and R i5 The measurement of R c3 and R i3 The measurement method was referred to.

[0060] Measurement of the area of ​​the primary and secondary particles and calculation of the area percentage: Calculate the area of ​​the particles using the software ImageJ and recognize the R c / R i The ratio was used to determine whether the particle belonged to the first particle or the second particle, and the sum of the particles with different attributes was taken as the area of ​​the first particle or the second particle. The area percentage of the first particle was the area of ​​the first particle / the area of ​​the image × 100%, and the area percentage of the second particle was the area of ​​the second particle / the area of ​​the image × 100%.

[0061] Measurement of particle size of positive electrode active material: The particle size of the positive electrode active material was measured using a Malvern particle size analyzer. The positive electrode active material was dispersed in ethanol, ultrasonicated for 30 minutes, and then added to the Malvern particle size analyzer. In the volumetric particle size distribution of the positive electrode active material, from the smallest particle size, the particle size at which the cumulative volume reached 10% was Dv10 of the positive electrode active material, the particle size at which the cumulative volume reached 50% was Dv50 of the positive electrode active material, and the particle size at which the cumulative volume reached 90% was Dv90 of the positive electrode active material.

[0062] Determination of elemental content: In the SEM image of the cross section of the positive electrode piece obtained above, the secondary particles were identified based on the particle size and area of ​​the particles in the image, and then measured with an energy dispersive spectroscopy (EDS) to determine the doping elements and element contents.

[0063] The positive electrode material layer of the positive electrode piece washed with DMC was removed with a blade, and the positive electrode material was dissolved in a mixed solvent (for example, 0.4 g of the positive electrode active material was dissolved in a mixed solvent of 10 ml of aqua regia (a 1:1 mixture of nitric acid and hydrochloric acid by volume) and 2 ml of HF), diluted to 100 ml, and the element contents in the solution were measured using an inductively coupled plasma (ICP) analyzer.

[0064] Measurement of the pressed density of the cathode pieces: At 25°C, the lithium-ion battery was charged to 4.2V at a constant current of 0.5C, then charged at a constant voltage of 0.05C at 4.2V, and discharged to 2.8V at a constant current of 1C. The lithium-ion battery was disassembled, and the positive electrode pieces were washed with DMC and dried at 60°C for 2 hours. Five positive electrode pieces measuring 5cm x 5cm were cut and the thickness of each positive electrode piece was measured using a micrometer. The positive electrode layer was removed from the positive electrode pieces using a blade. The mass of the positive electrode layer was measured using a micrometer. The thickness of the positive electrode current collector after the positive electrode layer was removed was measured as dcm. The compressed density of the positive electrode layer was calculated using the following formula: Compressed density P = m / [25 × (d0-d)], unit: g / cm 3 .

[0065] The compression density of the positive electrode material layer is the average value of the compression densities of the positive electrode material layers of the five positive electrode pieces obtained by the above cutting.

[0066] Measurement of particle size in the positive electrode material layer: At 25°C, the lithium-ion battery was charged to 4.2V at a constant current of 0.5C, then charged at a constant voltage of 0.05C at 4.2V, and then discharged to 2.8V at a constant current of 1C. The lithium-ion battery was disassembled, and the disassembled positive and negative electrode pieces were baked in a vacuum at 400°C to powder, after which the particle size was measured using a particle size analyzer, and the values ​​of Dv10, Dv50, and Dv90 were obtained.

[0067] Here, Dv90 refers to the particle size at which the cumulative volume is 90% from the smallest particle size in the volume-based particle size distribution, Dv50 refers to the particle size at which the cumulative volume is 50% from the smallest particle size in the volume-based particle size distribution, and Dv10 refers to the particle size at which the cumulative volume is 10% from the smallest particle size in the volume-based particle size distribution.

[0068] Measurement of rate characteristics and 25°C cycle characteristics: (1) 25℃ 2C room temperature rate characteristics and 25℃ cycle characteristics At 25°C, the lithium-ion battery was charged to 4.2V at a constant current of 0.5C, and then charged at a constant voltage of 0.05C at 4.2V, and then discharged to 2.8V at a constant current of 0.2C. The discharge capacity was D 01 The lithium-ion battery was charged to 4.2 V at a constant current of 0.5 C, further charged at a constant voltage of 0.05 C at 4.2 V, and then discharged to 2.8 V at a constant current of 2 C. The discharge capacity was recorded as D1. 25°C 2C rate retention rate (%) = D1 / D 01 ×100%.

[0069] Following the above operation steps, the lithium-ion battery was cycled through a cycle of "0.5C charge - 2C discharge" several times, and the discharge capacity after the 1000th cycle was measured. 10 The capacity retention rate after 1000 cycles at 25°C (%) = D 10 / D 01 ×100%.

[0070] (2) -10℃ 1C low temperature rate characteristics At 25°C, the lithium-ion battery was charged to 4.2V at a constant current of 0.5C, and then charged at a constant voltage of 0.05C at 4.2V, and then discharged to 2.8V at a constant current of 1C. The discharge capacity was D 02The lithium-ion battery was charged to 4.2 V at a constant current of 0.5 C at 25°C, and then further charged at a constant voltage of 0.05 C at 4.2 V. The temperature was adjusted to -10°C, and the cell was left for 30 minutes. After that, it was discharged to 2.8 V at a constant current of 1 C, and the discharge capacity was recorded as D2. -10°C 1C rate retention rate (%) = D2 / D 02 ×100%.

[0071] Measurement of cycle characteristics: 40℃ 500 cycles capacity retention rate: The lithium-ion battery was charged at 40°C with a constant current of 0.5C to 4.2V, then charged at a constant voltage until the current reached 0.05C, left for 5 minutes, and then discharged at a constant current of 1C to 2.8V, which constituted one charge-discharge cycle. The discharge capacity was D 03 The lithium ion battery was cycled 500 times according to the above operation steps, and the discharge capacity after the 500th cycle was measured as D3. The capacity retention rate after 500 cycles at 40°C (%) = D3 / D 03 ×100%.

[0072] Determination of manganese content in anode pieces: After 500 cycles at 40°C and complete discharge, the lithium-ion battery was disassembled, the negative electrode pieces were removed, washed with DMC, and dried at 60°C for 2 hours. The negative electrode material layer on the negative electrode pieces was then removed with a blade and dissolved in a mixed solvent (e.g., 0.4 g of negative electrode active material + 10 ml of aqua regia (a 1:1 mixture of nitric acid and hydrochloric acid by volume)), diluted to 100 ml, and the manganese content in the solution was measured using an ICP analyzer.

[0073] Example 1-1 <Preparation of positive electrode piece> 203.3 kg of lithium carbonate (where the mass fraction of lithium element is 18.71%), R c3 / R i31000 kg of manganese dioxide (wherein the mass fraction of Mn element is 60.22%) with an average value of 2.9 and a Dv50 of 17.2 μm, and 56.2 kg of aluminum oxide (Al2O3, the mass fraction of aluminum element is 52.91%), a compound containing M2 metal element, were weighed out and mixed in a high-speed mixer at a rotation speed of 300 r / min for 20 minutes to obtain a mixture. The mixture was then placed in an air kiln, heated to 790°C at a rate of 5°C / min, maintained at this temperature for 24 hours, naturally cooled, removed, and sieved through a 300-mesh sieve to obtain a manganese-containing complex metal oxide, i.e., LMO. c3 is the radius of the smallest circumscribing circle of the manganese dioxide particle outline, and R i3 is the radius of the largest inscribed circle around the outline of the manganese dioxide particle.

[0074] The positive electrode active material LMO, the conductive agent SuperP, and the binder polyvinylidene fluoride were mixed in a mass ratio of 96:2.4:1.6, and N-methylpyrrolidone (NMP) was added. The mixture was stirred using a vacuum mixer until homogeneous, yielding a positive electrode slurry. The solids content of the positive electrode slurry was 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm-thick aluminum foil current collector, and the aluminum foil was dried at 85°C to obtain a positive electrode piece coated with a positive electrode material layer on one side with a coating layer thickness of 110 μm. The above steps were repeated on the other surface of the aluminum foil, yielding a positive electrode piece coated with a positive electrode material layer on both sides. The piece was then cold-rolled, cut, slit, and dried under vacuum at 85°C for 4 hours, yielding a positive electrode piece measuring 74 mm x 867 mm. The positive electrode active material R c / R i The average value of was 2.9, and Dv50 was 17.9 μm.

[0075] <Preparation of negative electrode pieces> The negative electrode active material (artificial graphite), the conductive agent (SuperP), the thickener (sodium carboxymethylcellulose (CMC)), and the binder (styrene butadiene rubber (SBR)) were mixed in a mass ratio of 96.4:1.5:0.5:1.6, and deionized water was added. The negative electrode slurry was obtained using a vacuum mixer. The solids content of the negative electrode slurry was 70 wt%. The negative electrode slurry was uniformly coated onto one surface of a 10 μm-thick copper foil negative electrode current collector. The copper foil was dried at 85°C to obtain a negative electrode piece with a 130 μm-thick coating layer on one side. The above steps were repeated on the other surface of the copper foil, resulting in a negative electrode piece with a double-coated negative electrode layer. The negative electrode piece was then cold-rolled, cut, slit, and dried under vacuum at 120°C for 12 hours, yielding a 79 mm x 972 mm negative electrode piece.

[0076] <Preparation of electrolyte> In an argon atmosphere glove box with a water content of <10 ppm, a chain carbonate ester, DEC, and a cyclic carbonate ester, EC, were mixed in a mass ratio of 57.5:30 to obtain a base solvent. The lithium salt, LiPF6, was dissolved in the base solvent and mixed uniformly. Here, the mass fraction of LiPF6 relative to the mass of the electrolyte was 12.5%, and the remainder was the base solvent.

[0077] <Preparation of separator> Aqueous polyvinylidene fluoride, aluminum oxide, and polypropylene were mixed in a mass ratio of 1:8:1, added to deionized water, and stirred to obtain a coating layer slurry with a solids content of 50 wt%. The coating layer slurry was uniformly coated onto one surface of a 5 μm-thick PE film (Celgard) and dried at 85°C to obtain a separator with a coating layer coated on one side and a 5 μm-thick coating layer. The above steps were repeated on the other surface of the separator, resulting in a separator with coating layers applied to both sides. After drying and cold rolling, the separator was obtained. The porosity of the separator was 39%.

[0078] <Preparation of lithium-ion batteries> The positive electrode pieces, separator, and negative electrode pieces prepared above were stacked and wound up in order, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly was placed in an aluminum-plastic film packaging bag, dried, and then filled with electrolyte. The resulting lithium-ion battery was then vacuum-packaged, allowed to stand, formed (chemically formed), degassed, and cut. The formation conditions were charging to 3.3 V at a constant current of 0.02 C, followed by further charging to 3.6 V at a constant current of 0.1 C.

[0079] Examples 1-2 to 1-4 In Examples 1-2 to 1-4, the positive electrode active material R c / R i The average value of R of manganese dioxide and Dv50 are shown in Table 1. c3 / R i3 The results were the same as in Example 1-1, except that the average value of and Dv50 were adjusted.

[0080] Examples 1-5 and 1-6 In Examples 1-5 and 1-6, the raw material manganese dioxide was changed to trimanganese tetraoxide in the preparation of LMO, and the R of the positive electrode active material was c / R i The R of trimanganese tetraoxide was adjusted so that the average value of and Dv50 were the values ​​shown in Table 1. c4 / R i4 The results were the same as in Example 1-1, except that the average value of R and Dv50 were adjusted. c4 is the radius of the smallest circumscribing circle of the manganese dioxide particle, and R i4 is the radius of the maximum inscribed circle of the contour of the manganese dioxide particle.

[0081] Example 2-1 In Example 2-1, in <Preparation of Positive Electrode Pieces>, the positive electrode active material is LMO, the positive electrode active material is LiNi 0.55 Co 0.15 Mn 0.3O2 (NCM5515), conductive agent SuperP, and binder polyvinylidene fluoride were mixed in a mass ratio of 76.8:19.2:2.4:1.6, and NMP was added. The mixture was stirred with a vacuum mixer until it was homogenous, resulting in a positive electrode slurry with a solid content of 75 wt%. c / R i and the R of manganese dioxide so that the average value of Dv50 of the positive electrode active material becomes the value shown in Table 2. c3 / R i3 The results were the same as in Example 1-1, except that the average value of and Dv50 were adjusted.

[0082] The above NCM5515 was obtained by the following method: lithium carbonate (wherein the mass fraction of lithium element is 18.71%), and R c5 / R i5 The average value of Dv50 is 1.2 and Dv50 is 16.3μm. 0.55 Co 0.15 Mn 0.3 The (OH) precursor was mixed for 20 minutes at a rotation speed of 300 r / min in a high-speed mixer so that the ratio of moles of Li to moles of transition metal elements (total moles of Ni, Co, and Mn) was 1.05:0.997. The mixture was then placed in an oxygen gas furnace, heated to 890°C at a rate of 5°C / min, maintained at this temperature for 12 hours, and then naturally cooled. After removal, the mixture was sieved through a 300-mesh sieve to obtain lithium nickel cobalt manganese oxide (NCM5515). c5 Ni 0.55 Co 0.15 Mn 0.3 is the radius of the smallest circumscribing circle of the (OH) precursor particle outline, R i5 Ni 0.55 Co 0.15 Mn 0.3 is the radius of the largest inscribed circle of the outline of the (OH)2 precursor particle.

[0083] Examples 2-2 to 2-4, and 2-7 In Examples 2-2 to 2-4 and 2-7, the corresponding positive electrode active materials were mixed according to Table 2, and R c3 / R i3 Average value of Dv50 and / or Ni0.55 Co 0.15 Mn 0.3 (OH)2 precursor R c5 / R i5 The mean value of the R c1 / R i1 The average value of R c2 / R i2 The average value of the area percentage of the first particles, the area percentage of the second particles, the Dv50 of the positive electrode active material, and the particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode active material are shown in Table 2, and the other values ​​were the same as in Example 2-1. 0.6 Co 0.1 Mn 0.3 O2, and NCM8309 is LiNi 0.83 Co 0.09 Mn 0.08 The ratio of the number of moles of Li to the number of moles of transition metal elements in the preparation of NCM5515 was adjusted so that NCM6010 and NCM8309 would satisfy the above chemical formula.

[0084] Examples 2-5 and 2-6 In Examples 2-5 and 2-6, in the preparation of the first particle LMO, the raw material manganese dioxide was changed to trimanganese tetraoxide, and the R c4 / R i4 The average value and Dv50 of the manganese dioxide in the preparation of the second particle LMO were adjusted. c3 / R i3 The average value and Dv50 of c1 / R i1 The average value of R c2 / R i2 The average value of the particle diameter, the area percentage of the first particles, the area percentage of the second particles, the Dv50 of the positive electrode active material, and the particle diameter distribution (Dv90-Dv10) / Dv50 of the positive electrode active material are shown in Table 2, and the rest were the same as in Example 2-1.

[0085] Examples 3-1 to 3-7 Examples 3-1 to 3-7 were the same as Example 2-1, except that the types and contents of the chain carbonate ester and cyclic carbonate ester were adjusted according to Table 3 to obtain the base solvent.

[0086] Examples 4-1 to 4-9 Examples 4-1 to 4-9 were the same as Example 2-1, except that in <Preparation of Electrolyte Solution>, a sulfonate ester compound was further added to the electrolyte solution, and the type and mass fraction of the sulfonate ester compound were adjusted according to Table 4.

[0087] Examples 5-1 to 5-6 Examples 5-1 to 5-6 were similar to Example 2-1, except that during the LMO preparation process, an M2 metal element-containing compound was added according to Table 5, and the content was adjusted so that the mass fraction of the metal element M2 was the value shown in Table 5.

[0088] Examples 5-7 Example 5-7 was the same as Example 5-3, except that commercially available LiFePO4 (referred to as LFP) with a Dv50 of 1.0 μm was used instead of NCM5515.

[0089] Examples 5-8 In Examples 5-8, instead of NCM5515, commercially available LiMn 0.75 Fe 0.25 The procedure was the same as in Example 5-3, except that PO4 (referred to as LMFP) was used.

[0090] Examples 5-9 Example 5-9 was the same as Example 5-3, except that a commercially available LFP with a Dv50 of 1.0 μm was used in place of part of the NCM5515, and the mass ratio of LMO, NCM5515, LFP, SuperP, and polyvinylidene fluoride was 76.8:9.2:10:2.4:1.6.

[0091] Comparative Example 1 Comparative Example 1 is R c / R iThe results were the same as in Example 1-1, except that the average values ​​of .DELTA..times ...

[0092] Tables 1 to 5 show the preparation parameters and performance measurements for each example and comparative example.

[0093] [Table 1]

[0094] As can be seen from Examples 1-1 to 1-6 and Comparative Example 1, R c / R i When the value of is within the range of the present invention, the resulting lithium ion battery has good low-temperature rate characteristics and room-temperature rate characteristics at the same time.

[0095] [Table 2]

[0096] The area percentage of the first particles, the area percentage of the second particles, the Dv50 of the positive electrode active material, and the value of (Dv90-Dv10) / Dv50 generally affect the performance of a lithium ion battery. As can be seen from Examples 2-1 to 2-7, when the area percentage of the first particles, the area percentage of the second particles, the Dv50 of the positive electrode active material, and the value of (Dv90-Dv10) / Dv50 are within the ranges of the present invention, the resulting lithium ion battery has good low-temperature rate characteristics and room-temperature rate characteristics.

[0097] [Table 3]

[0098] The types and mass fractions of the chain carbonate ester and cyclic carbonate ester in the electrolyte, as well as the value of ω1 / ω2, generally affect the performance of a lithium-ion battery. As can be seen from Examples 2-1 and 3-1 to 3-7, when the types and mass fractions of the chain carbonate ester and cyclic carbonate ester, as well as the value of ω1 / ω2, are within the ranges of the present invention, the resulting lithium-ion battery has good low-temperature rate characteristics.

[0099] [Table 4]

[0100] As can be seen from Examples 2-1 and 4-1 to 4-9, adding a sulfonate ester compound to the electrolyte can improve the high-temperature cycle characteristics of lithium-ion batteries and the manganese elution phenomenon on the negative electrode pieces. As can be seen from Examples 4-1 to 4-9, when the type and mass fraction of the sulfonate ester compound are within the ranges of the present invention, the resulting lithium-ion battery has good high-temperature cycle characteristics and little manganese elution on the negative electrode pieces. In addition, when the A / B value is within the range of the present invention, the resulting lithium-ion battery has good high-temperature cycle characteristics and little manganese elution on the negative electrode pieces.

[0101] [Table 5]

[0102] The type of element in the positive electrode active material generally affects the performance of a lithium ion battery. As can be seen from Examples 2-1 and 5-1 to 5-9, when the positive electrode active material contains Mn and the metal element M1, the resulting lithium ion battery has good low-temperature rate characteristics. Furthermore, when the second particles contain the metal element M2 and the type and mass fraction thereof are within the ranges of the present invention, the resulting lithium ion battery has good low-temperature rate characteristics.

[0103] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An electrochemical device including a positive electrode piece, the positive electrode piece including a positive electrode material layer, the positive electrode material layer including a positive electrode active material; In a scanning electron microscope photograph of a cross section of the positive electrode material layer, an area of ​​5 μm ２ The radius of the smallest circumscribing circle of the contour of the positive electrode active material particle is R ｃ and the area is 5 μm ２ The radius of the maximum inscribed circle of the contour of the positive electrode active material particle is R ｉ When this is done, R ｃ and R ｉ is 1<R ｃ / R ｉ The average value of ≦3 is satisfied, the electrochemical device further comprises an electrolyte; the electrolyte solution contains a chain carbonate ester and a cyclic carbonate ester, The mass fraction of the chain carbonate ester relative to the mass of the electrolyte solution is ω １ and the mass fraction of the cyclic carbonate is ω ２ When this is done, ω ２ is 25% to 50%, and ω １ / ω ２ is 0.75 to 2.5, the positive electrode active material particles having an area of ​​more than 5 μm 2 include first particles and second particles; When the radius of the smallest circumscribing circle of the outline of the first particle is R c1 and the radius of the largest inscribing circle of the outline of the first particle is R i1 , R c1 and R i1 satisfy the relationship 1<average value of R c1 / R i1 ≦1.5, When the radius of the smallest circumscribing circle of the outline of the second particle is R c2 and the radius of the largest inscribing circle of the outline of the second particle is R i2 , R c2 / R i2 satisfies 1.5<average value of R c2 / R i2 ≦3, With respect to a cross-sectional area of ​​the positive electrode material layer, an area percentage of the first particles is more than 0% and 50% or less, and an area percentage B of the second particles is 30% to 80%; the average cross-sectional area of ​​the first particles is smaller than the average cross-sectional area of ​​the second particles; An electrochemical device that satisfies at least one of the above.

2. (a) the positive electrode active material contains lithium manganese oxide; (b) the positive electrode active material includes a composite metal oxide of a lithium element and a transition metal element, the transition metal element includes Mn and a metal element M1, and the metal element M1 includes at least one of Ni, Co, and Fe; The electrochemical device according to claim 1 , which satisfies at least one of the following conditions:

3. The electrochemical device described in claim 1, wherein the second particles contain a metal element M2, and the metal element M2 contains at least one of Al, Mg, and Nb.

4. An electrochemical device as described in claim 1, wherein the second particles contain a metal element M2, and the mass fraction of the metal element M2 is 0.1% to 3% relative to the mass of the second particles.

5. The volume particle size distribution of the positive electrode active material is (c) 9 μm≦Dv50≦22 μm; (d) 0.9≦(Dv90−Dv10) / Dv50≦2; The electrochemical device according to claim 1 , which satisfies at least one of the following conditions:

6. 2. The electrochemical device according to claim 1, wherein the chain carbonate ester includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, and dibutyl carbonate.

7. 2. The electrochemical device according to claim 1, wherein the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

8. 2. The electrochemical device according to claim 1, wherein the electrolytic solution contains a sulfonate ester compound, and when A represents a mass fraction of the sulfonate ester compound relative to the mass of the electrolytic solution, A and B satisfy a relationship of 0.006≦A / B≦0.

1.

9. The electrochemical device according to claim 8 , wherein 0.5%≦A≦10% is satisfied.

10. The sulfonate ester compound is 【Chemistry 1】 The electrochemical device according to claim 8 , comprising at least one of:

11. further comprising a negative electrode piece; 2. The electrochemical device according to claim 1, wherein the negative electrode piece includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite, natural graphite, and hard carbon.

12. An electronic device comprising an electrochemical device according to any one of claims 1 to 11.

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