Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device, the electrochemical device comprises a positive pole piece, the positive pole piece comprises a positive pole material layer, the positive pole material layer comprises a positive pole active material, in a scanning electron microscope picture of the section of the positive pole material layer, the radius of the minimum circumcircle of the contour of positive pole active material particles with the area larger than 5 mu m < 2 > is Rc, the radius of the maximum inscribed circle of the outlines of the positive electrode active material particles having an area greater than 5 [mu] m2 is Ri, and an average value of 1 < Rc / Ri < = 3 is satisfied. According to the electrochemical device provided by the invention, the positive electrode active material in the positive electrode material layer meets the condition that the average value of Rc / Ri is greater than 1 and less than or equal to 3, and the transmission efficiency of lithium ions can be effectively improved, so that the rate capability of the electrochemical device at normal temperature and low temperature is improved.

Description

[0001] This application is a divisional application of the Chinese patent application with the application number 202180046458.9 and the invention title "An Electrochemical Device and an Electronic Device", which was filed with the Patent Office of the State Intellectual Property Office of China on December 15, 2021. Technical Field

[0002] This application relates to the field of electrochemistry, and particularly to an electrochemical device and an electronic device. Background Art

[0003] Lithium-ion batteries have been widely used in fields such as wearable devices, smart phones, drones, electric vehicles, and large-scale energy storage devices due to their advantages such as high energy density, long cycle life, and no memory effect, and have become the most promising new green chemical power sources in the world today. However, with the wide application of lithium-ion batteries, the market has put forward higher requirements for the comprehensive performance of lithium-ion batteries.

[0004] The positive electrode active material, negative electrode active material, and electrolyte in a lithium-ion battery are important parameters affecting the performance of the lithium-ion battery. Among them, the selection of the positive electrode active material will affect the transmission efficiency of lithium ions, thereby affecting the electrochemical performance of the electrochemical device, such as the rate performance. However, the existing positive electrode active materials need to be further optimized to improve the rate performance of the electrochemical device. Summary of the Invention

[0005] The purpose of this application is to provide an electrochemical device and an electronic device to improve the rate performance of the electrochemical device at low temperature and normal temperature.

[0006] The first aspect of this application provides an electrochemical device, which includes a positive electrode tab. The positive electrode tab includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material. In the scanning electron microscope photograph of the cross-section of the positive electrode material layer, the radius of the minimum circumscribed circle of the contour of the positive electrode active material particles with an area greater than 5 μm 2 is R c , and the radius of the maximum inscribed circle of the contour of the positive electrode active material particles with an area greater than 5 μm 2 is R i , satisfying 1 < R c / R i The average value of ≤ 3. For example, the average value of R c / R i can be 1.1, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3 or any range therebetween. Without being limited to any theory, for the electrochemical device provided in this application, among them, the positive electrode active material in the positive electrode material layer satisfies 1 < R c / R iThe average value of ≤ 3 can effectively improve the transport efficiency of lithium ions during charge and discharge, thereby improving the rate performance of the electrochemical device at room temperature and low temperature (for example, the temperature is less than or equal to 0 °C). This may be because, R c / R i For the positive electrode material layer with the average value within the above range, its morphology enables the positive electrode active material to maintain a stable crystal structure during cycling at a large rate, and effectively improves the lithium ion insertion and extraction kinetics of the positive electrode active material, providing good lithium ion transport performance, thereby improving the rate performance of the electrochemical device. In this application, the cross-section of the positive electrode material layer refers to the cross-section obtained by cutting along the thickness direction of the positive electrode material layer.

[0007] In some embodiments of this application, the positive electrode active material particles with an area greater than 5 μm 2 include first particles and second particles. The radius of the minimum circumscribed circle of the contour of the first particles is R c1 , and the radius of the maximum inscribed circle of the contour of the first particles is R i1 , satisfying 1 < R c1 / R i1 The average value of ≤ 1.5; the radius of the minimum circumscribed circle of the contour of the second particles is R c2 , and the radius of the maximum inscribed circle of the contour of the second particles is R i2 , satisfying 1.5 < R c2 / R i2 The average value of ≤ 3.

[0008] Based on the cross-sectional area of the positive electrode material layer, the area percentage of the first particles is greater than 0% and less than or equal to 50%, and the area percentage B of the second particles is 30% to 80%. For example, R c1 / R i1 The average value of can be 1.1, 1.2, 1.3, 1.4, 1.5 or any range therebetween; R c2 / R i2 The average value of can be 1.6, 2, 2.5, 3 or any range therebetween; the area percentage of the first particles can be 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any range therebetween; the area percentage B of the second particles can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or any range therebetween.

[0009] The first particles and the second particles are distributed in the positive electrode material layer in the above ratio. After the compaction process, different R in the positive electrode material layer is achieved c / R iThe interlaced distribution of particles with values improves the distribution network of the positive electrode active material and the conductive agent, thereby effectively reducing the interfacial side reactions within the positive electrode material layer while improving the lithium ion transport efficiency and the electronic conductivity inside the positive electrode sheet, achieving effective improvement of the rate performance and cycle performance of the electrochemical device. When the area percentage B of the second particles is too small (for example, less than 30%), the area percentage of the first particles is too large, and the tap density of the positive electrode sheet decreases, affecting the lithium ion transport efficiency; when the area percentage B of the second particles is too large (for example, greater than 80%), it will also cause the tap density of the positive electrode sheet to decrease, affecting the lithium ion transport efficiency, thereby affecting the rate performance of the electrochemical device at normal and low temperatures. By regulating the area percentages of the first particles and the second particles within the scope of this application, it is beneficial to improve the rate performance of the electrochemical device at normal and low temperatures. In this application, the tap density of the positive electrode sheet refers to the tap density of the positive electrode material layer in the positive electrode sheet.

[0010] In some embodiments of this application, the average cross-sectional area of the first particles is smaller than that of the second particles, which is beneficial to reducing the lithium ion transport path and improving the rate performance of the electrochemical device.

[0011] In some embodiments of this application, the electrochemical device satisfies at least one of the conditions (a) to (b): (a) The positive electrode active material includes lithium manganate; the lithium manganate includes doped lithium manganate and / or lithium manganate with a coating layer. There is no particular limitation on the doping element in the doped lithium manganate in this application, as long as the purpose of this application can be achieved. For example, the doping element may include, but is not limited to, at least one of Al, Nb, Mg, Ti, F, B, Zr, W, Sr, Y, Ce, or La. There is no particular limitation on the elements in the coating layer of the lithium manganate with a coating layer in this application, as long as the purpose of this application can be achieved. For example, the elements in the coating layer may include, but is not limited to, at least one of Al, Sr, Zr, Ti, or B. (b) The positive electrode active material includes a composite metal oxide of lithium element and transition metal elements, the transition metal elements include Mn and metal element M1, and the metal element M1 includes at least one of Ni, Co, or Fe. Based on the mass of the positive electrode active material, the mass percentage content of Mn is 30% to 65%, and the mass percentage content of the metal element M1 is 2% to 25%. The electrochemical device satisfying at least one of the conditions (a) to (b) is beneficial to improving the cycle performance and low-temperature rate performance of the electrochemical device.

[0012] In some embodiments of this application, the second particles include metal element M2, and the metal element M2 includes at least one of Al, Mg, or Nb.

[0013] In some embodiments of the present application, based on the mass of the second particles, the mass percentage of the metal element M2 is from 0.1% to 3%. For example, the mass percentage of the metal element M2 can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.5%, 3% or any range therebetween.

[0014] In the related art, manganese-containing positive electrode active materials (such as lithium manganate) are widely used in electrochemical devices, such as lithium-ion batteries. However, the Mn 3+ in lithium manganate is prone to disproportionation reaction, resulting in the dissolution of manganese (Mn 2+ ), which then migrates to the negative electrode through the electrolyte, breaking the solid electrolyte interface (SEI) film of the negative electrode. Repairing the SEI film causes loss of active lithium, thereby affecting the cycle performance and rate performance of the lithium-ion battery. In the present application, the negative electrode may refer to the negative electrode plate.

[0015] The inventors of the present application have found that for an electrochemical device including a manganese-containing positive electrode active material, when the positive electrode active material includes the metal element M1, by selecting the above metal element M1, it is beneficial to improve the manganese dissolution phenomenon, thereby reducing the damage to the negative electrode SEI film and the loss of active lithium caused by the consumption of lithium for repairing the SEI film, thereby improving the cycle performance and rate performance of the electrochemical device.

[0016] The inventors of the present application have found that when the second particles include the metal element M2, by selecting the above metal element M2, the interfacial side reaction between the second particles and the electrolyte during low-temperature charge and discharge can be reduced, thereby improving the internal resistance of the positive electrode plate and enhancing the low-temperature rate performance of the electrochemical device.

[0017] The inventors of the present application have found that when the mass percentage of the metal element M2 is too low (for example, less than 0.1%), the improvement of the side reaction between the second particles and the electrolyte is not obvious. When the mass percentage of the metal element M2 is too high (for example, higher than 3%), while the side reaction between the second particles and the electrolyte cannot be further improved, the specific capacity per gram of the positive electrode active material will be reduced. By controlling the mass percentage of the metal element M2 within the above range, it is beneficial to reduce the interfacial side reaction between the second particles and the electrolyte and improve the cycle performance of the electrochemical device. In the present application, the negative electrode may refer to the negative electrode plate.

[0018] In some embodiments of the present application, the volume particle size distribution of the positive electrode active material satisfies at least one of the conditions (c) to (d): (c) 9 μm ≤ Dv50 ≤ 22 μm; (d) 0.9 ≤ (Dv90 - Dv10) / Dv50 ≤ 2. For example, Dv50 of the positive electrode active material can 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, 22 μm or any range therebetween. For example, the value of (Dv90 - Dv10) / Dv50 can be 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2 or any range therebetween. By controlling the volume particle size distribution of the positive electrode active material to satisfy at least one of the conditions (c) to (d), it is beneficial to improve the rate performance of the electrochemical device at room temperature and low temperature. The present application does not particularly limit Dv90 and Dv10 of the positive electrode active material, as long as the value of (Dv90 - Dv10) / Dv50 is within the above range. For example, Dv90 of the positive electrode active material is 15 μm to 40 μm, and Dv10 of the positive electrode active material is 0.5 μm to 6 μm. Among them, the value of (Dv90 - Dv10) / Dv50 mainly reflects the particle size distribution of the positive electrode active material.

[0019] In some embodiments of the present application, the electrochemical device further includes an electrolyte, and the electrolyte includes a chain carbonate and a cyclic carbonate. Based on the mass of the electrolyte, the mass percentage content of the chain carbonate is ω1, and the mass percentage content ω2 of the cyclic carbonate is 25% to 50%, satisfying ω1 / ω2 being 0.75 to 2.5. For example, the mass percentage content ω2 of the cyclic carbonate can be 25%, 30%, 35%, 40%, 45%, 50% or any range therebetween; the value of ω1 / ω2 can be 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5 or any range therebetween.

[0020] Without being limited to any theory, when regulating the average value of R c / R i in the positive electrode active material, the electrolyte includes a chain carbonate and a cyclic carbonate, so that a synergistic effect is generated between the positive electrode active material and the electrolyte, which can improve the lithium ion transport path, especially the lithium ion transport efficiency at the interface between the positive electrode active material and the electrolyte, thereby improving the rate performance of the electrochemical device.

[0021] Without being limited to any theory, when the mass percentage content ω2 of the cyclic carbonate is too low (for example, less than 25%), the cyclic carbonate cannot form a good synergistic effect with the linear carbonate to improve the lithium ion transport efficiency; when the mass percentage content ω2 of the cyclic carbonate is too high (for example, higher than 50%), it causes an increase in the viscosity of the electrolyte, which is not conducive to the transport of lithium ions, thus affecting the rate performance of the electrochemical device. When the value of ω1 / ω2 is less than 0.75 or greater than 2.5, the synergistic effect between the cyclic carbonate and the linear carbonate will be affected, thereby affecting the lithium ion transport efficiency. By regulating the mass percentage content ω2 of the cyclic carbonate and the value of ω1 / ω2 within the scope of the present application, the positive electrode active material can be fully wetted, 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.

[0022] In some embodiments of the present application, 35% ≤ ω1 ≤ 65%. For example, the mass percentage content ω1 of the linear carbonate can be 35%, 40%, 45%, 50%, 55%, 60%, 65% or any range therebetween. Without being limited to any theory, by regulating the mass percentage content ω1 of the linear carbonate within the scope of the present application, it is beneficial to form a good synergistic effect between the cyclic carbonate and the linear carbonate, improve the lithium ion transport efficiency, and thus improve the rate performance of the electrochemical device.

[0023] In some embodiments of the present application, the linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), methyl isopropyl carbonate, methyl butyl carbonate or dibutyl carbonate (DBC). Without being limited to any theory, by selecting the above linear carbonate, it is beneficial to improve the lithium ion transport efficiency and improve the rate performance of the electrochemical device.

[0024] In some embodiments of the present application, the cyclic carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC) or butylene carbonate (BC). Without being limited to any theory, by selecting the above cyclic carbonate, it is beneficial to improve the lithium ion transport efficiency and improve the rate performance of the electrochemical device.

[0025] In some embodiments of the present application, the electrolyte includes a sulfonate compound. Based on the mass of the electrolyte, the mass percentage of the sulfonate compound is A, and 0.006 ≤ A / B ≤ 0.1 is satisfied. For example, the value of A / B can be 0.006, 0.008, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1 or any range therebetween. Without being limited to any theory, the sulfur-oxygen double bond in the sulfonate compound is beneficial to improving the stability of the SEI film, reducing the deposition of dissolved manganese on the negative electrode, and thus improving the cycling performance of the electrochemical device. At the same time, when the value of A / B is within the range of the present application, it is beneficial to generate a synergistic effect between the sulfonate compound and the positive electrode active material, improve the lithium ion transport efficiency while improving the stability of the SEI film, and further improve the rate performance of the electrochemical device.

[0026] In some embodiments of the present application, 0.5% ≤ A ≤ 10%. For example, the mass percentage A of the sulfonate compound can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range therebetween. Without being limited to any theory, when the mass percentage A of the sulfonate compound is too low (e.g., less than 0.5%), the improvement of the SEI film stability is not obvious; when the mass percentage A of the sulfonate compound is too high (e.g., higher than 10%), an overly thick or overly dense SEI film will be formed, hindering the lithium ion transport and resulting in a decrease in the rate performance of the electrochemical device.

[0027] Preferably, the sulfonate compound includes at least one of the following structural compounds I-1 to I-14. By selecting the sulfonate compound with the following structure, it is beneficial to improve the stability of the SEI film, reduce the deposition of dissolved manganese on the negative electrode, and thus improve the cycling performance of the electrochemical device.

[0028]

[0029]

[0030] In some embodiments of the present application, 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, or hard carbon. Without being limited to any theory, by selecting the above negative electrode active material, it is more beneficial to form a synergistic effect with the aforementioned positive electrode active material and / or electrolyte to improve the cycling performance and rate performance of the electrochemical device.

[0031] In the present application, the positive electrode active material may include, but is not limited to, at least one of a composite oxide and / or a sulfide, selenide, or halide of the composite oxide. The composite oxide may include, but is not limited to, LiMn2O4, Li(Ni a1 Cob1 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) or LiMn p Fe q PO4 (0 < p < 1, 0 < q < 1, p + q = 1) or at least one of LiFePO4.

[0032] Optionally, an amorphous compound or a crystalline compound may also be present on the surface of the composite oxide. 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, a hydroxy-oxide of element Z, a carbonate-oxide of element Z, or a basic carbonate of element Z. Among them, 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, or Zr.

[0033] The present application does not particularly limit the preparation method of the composite oxide having an amorphous compound or a crystalline compound on the surface, as long as the object of the present application can be achieved, such as a spraying method or an impregnation method, etc.

[0034] In the present application, the positive electrode material layer may further include a conductive agent. The present application does not particularly limit the conductive agent, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metal materials, or conductive polymers. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above metal materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. In the present application, based on the mass of the positive electrode material layer, the mass percentage content of the conductive agent is 0.5% to 5%.

[0035] In this application, the positive electrode material layer may further include a positive electrode binder. There is no particular limitation on the positive electrode binder in this application, as long as the purpose of this application can be achieved. For example, it may include but is not limited to at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0036] In this application, the positive electrode plate includes a positive electrode current collector. Among them, there is no particular limitation on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it may include but is not limited to aluminum foil, aluminum alloy foil, or a composite current collector, etc. In this application, there is no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness is 8 μm to 20 μm.

[0037] Optionally, the positive electrode plate may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. There is no particular limitation on the composition of the conductive layer in this application. It can be a commonly used conductive layer in the art. For example, it may include but is not limited to the above-mentioned conductive agent and the above-mentioned positive electrode binder.

[0038] In this application, the negative electrode material layer may further include a conductive agent. There is no particular limitation on the conductive agent in this application, as long as the purpose of this application can be achieved. For example, it may include but is not limited to at least one of the above-mentioned conductive agents.

[0039] In this application, the negative electrode material layer may further include a negative electrode binder. There is no particular limitation on the negative electrode binder in this application, as long as the purpose of this application can be achieved. For example, it may include but is not limited to at least one of vinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0040] In this application, the negative electrode plate includes a negative electrode current collector. Among them, there is no particular limitation on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector, etc. In this application, there is no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness is 4 μm to 12 μm.

[0041] Optionally, the negative electrode sheet may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. The conductive layer may include, but is not limited to, the above-mentioned conductive agent and the above-mentioned negative electrode binder.

[0042] In the present application, the electrolyte may further include a non-aqueous solvent. The present application does not particularly limit the non-aqueous solvent, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, at least one of carboxylic ester compounds, ether compounds, or other organic solvents. The above-mentioned carboxylic ester compounds may include, but are not limited to, at least one of 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, trifluoroethyl acetate, 2,2,3,3,3-pentafluoropropyl acetate, 2,2,3,3,4,4,4,4-octafluorobutyl methyl ester, 4,4,4-trifluoro-3-(trifluoromethyl)butyl methyl ester, 2,2,3,3,4,4,5,5,5,5-decafluoropentyl acetate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl methyl ester, or 2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,9-heptadecafluorononyl ethyl ester. The above-mentioned 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, or bis(2,2,2-trifluoroethyl) ether. The above-mentioned 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, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate ester.

[0043] In the present application, the electrolyte may further include a lithium salt. The present application does not particularly limit the lithium salt, as long as the object of the present application can be achieved. For example, it may include, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiB(C2O4)2), lithium difluoro(oxalato)borate (LiBF2(C2O4)), lithium hexafluoroantimonate (LiSbF6), lithium perfluorobutanesulfonate (LiC4F9SO3), lithium perchlorate (LiClO4), lithium aluminate (LiAlO2), lithium tetrachloroaluminate (LiAlCl4), lithium bis(sulfonyl)imide (LiN(C x F 2x+1 SO2)(C y F2y+1 SO2), where x and y are natural numbers less than or equal to 4), lithium chloride (LiCl), lithium fluoride (LiF), or at least one of them. Preferably, the lithium salt includes LiPF6. There is no particular limitation on the concentration of the lithium salt in this application, as long as the object of this application can be achieved. For example, the concentration can be 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.

[0044] The electrochemical device of this application further includes a separator. There is no particular limitation on the separator in this application, as long as the object of this application can be achieved. For example, it can include, but is not limited to, at least one of polyolefin (PO) separators mainly composed of polyethylene (PE), polypropylene (PP), polytetrafluoroethylene, polyester membranes (such as polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide membranes (PI), polyamide membranes (PA), spandex, aramid membranes, woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator papers, rolled membranes, or spun membranes. The separator of this application can have a porous structure, and there is no particular limitation on the size of the pore diameter, as long as the object of this application can be achieved. For example, the size of the pore diameter can be 0.01 μm to 1 μm. In this application, there is no particular limitation on the thickness of the separator, as long as the object of this application can be achieved. For example, the thickness can be 5 μm to 500 μm.

[0045] For example, the separator can include a separator substrate layer and a surface treatment layer. The separator substrate layer can be a non-woven fabric, a membrane, or a composite membrane with a porous structure. The material of the separator substrate layer can include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be used. Optionally, a surface treatment layer is provided on at least one surface of the separator substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0046] The polymer layer contains a polymer, and the material of the polymer may include, but is not limited to, at least one of vinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, polyacrylonitrile, polyimide, acrylonitrile - butadiene copolymer, acrylonitrile - styrene - butadiene copolymer, polymethyl methacrylate, poly(methyl acrylate), poly(ethyl acrylate), acrylic - styrene copolymer, polydimethylsiloxane, sodium polyacrylate, or carboxymethyl cellulose. The inorganic layer may include, but is not limited to, inorganic particles and an inorganic layer binder. There is no particular limitation on the inorganic particles in this application. For example, it may include, but is not limited to, at least one of ceramics, alumina, silica, magnesia, 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, or barium sulfate, etc. There is no particular limitation on the inorganic layer binder in this application. For example, it may include, but is not limited to, at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride - hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0047] There is no particular limitation on the electrochemical device of this application, and it may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to: lithium metal secondary battery, lithium - ion secondary battery (lithium - ion battery), lithium polymer secondary battery, or lithium - ion polymer secondary battery, etc.

[0048] The preparation process of the electrochemical device is well - known to those skilled in the art, and there is no particular limitation in this application. For example, it may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding or folding as needed to obtain a wound - structure electrode assembly. Then, putting the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or, stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then fixing the four corners of the entire laminated structure with tape to obtain a laminated - structure electrode assembly. Then, putting the electrode assembly into a packaging bag, injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. In addition, an over - current protection element, a guide plate, etc. may be placed in the packaging bag as needed to prevent the pressure inside the electrochemical device from rising and over - charge / discharge.

[0049] The second aspect of this application provides an electronic device, which includes the electrochemical device in any embodiment of this application. The electrochemical device provided by this application has good rate performance and cycling performance, so that the electronic device provided by this application has a long service life.

[0050] The electronic device of the present application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0051] The present application provides an electrochemical device, which includes a positive electrode tab. The positive electrode tab includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material. In a scanning electron microscope photograph of the cross-section of the positive electrode material layer, the radius of the minimum circumscribed circle of the contour of the positive electrode active material particles with a cross-sectional area greater than 5 μm 2 is R c and the radius of the maximum inscribed circle of the contour of the particles with a cross-sectional area greater than 5 μm 2 is R i and it satisfies 1 < R c / R i and the average value of ≤ 3. For the electrochemical device provided by the present application, the positive electrode active material in the positive electrode material layer satisfies 1 < R c / R i and the average value of ≤ 3, which can effectively improve the lithium-ion transport efficiency of the positive electrode tab, thereby improving the rate performance of the electrochemical device at room temperature and low temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions of the embodiments of the present application and the prior art, the following briefly introduces the drawings required to be used in the embodiments and the prior art. Obviously, the drawings in the following description are only some embodiments of the present application.

[0053] Figure 1 is a scanning electron microscope photograph of the cross-section of the positive electrode material layer in an embodiment of the present application;

[0054] Figure 2 is a schematic cross-sectional view of the positive electrode tab in an embodiment of the present application.

[0055] Reference numerals: 10, positive electrode current collector; 20, positive electrode material layer; 21, positive electrode active material. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0056] To make the objectives, technical solutions, and advantages of the present application clearer and more understandable, the following provides examples with reference to the accompanying drawings to further elaborate on the present application in detail. Apparently, the described embodiments are only a part of the embodiments of the present application, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application fall within the scope of protection of the present application.

[0057] Figure 1 The scanning electron microscope photograph of the cross-section of the positive electrode material layer in an embodiment of the present application is shown. It can be seen from the figure that there are differences in the size and shape of the particles of the positive electrode active material 21. The minimum circumscribed circle of the contour of particle C is R1, and the maximum inscribed circle of the contour of particle C is R2; the minimum circumscribed circle of the contour of particle D is R3, and the maximum inscribed circle of the contour of particle D is R4. Among them, particle C is an example of the first particle in the present application, and particle D is an example of the second particle in the present application.

[0058] Figure 2 The schematic cross-sectional view of the positive electrode plate in an embodiment of the present application is shown. There are positive electrode material layers 20 on both surfaces of the positive electrode current collector 10. 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 aforementioned positive electrode material layer in the present application refers to the cross-section obtained by transverse cutting along the direction of the arrow in the figure.

[0059] It should be noted that in the specific implementation manner of the present application, the average value of R c1 / R i1 of the first particle and the average value of R c2 / R i2 of the second particle can be controlled by controlling the ratio of the radius of the minimum circumscribed circle to the radius of the maximum inscribed circle of the contour of the raw material particles, as well as the Dv50 of the raw material, and comprehensively adjusting conditions such as the stirring speed or calcination temperature during the preparation process of the positive electrode active material.

[0060] It should be noted that in the specific implementation manner of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion batteries.

[0061] Embodiment

[0062] Hereinafter, examples and comparative examples are given to more specifically illustrate the implementation manner of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0063] Testing methods and equipment:

[0064] R i and R c Measurement:

[0065] At 25 °C, the lithium-ion battery is charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C, and then discharged at a constant current of 1C to 2.8V. The lithium-ion battery is disassembled, and the positive electrode plate is cleaned with DMC, and then dried at 60 °C for 2h; the positive electrode plate is cut along the thickness direction of the positive electrode plate itself using an ion polishing instrument to obtain a flat cross-section of the positive electrode plate; the cross-section is tested using a scanning electron microscope (SEM); an SEM image with a magnification of 1000 times is selected.

[0066] The software Image J is used to identify the graphical morphology of the above SEM image. Randomly select 100 particles whose cross-sections are completely within the image field of view and whose cross-sectional areas are greater than 5μm 2 For the particles, the radius R of the largest inscribed circle of the particles is calculated using the algorithm i and the radius R of the smallest circumscribed circle c (refer to "Kenneth C. Williams, Wei Chen, Sebastian Weeger, Timothy J. Donohue, Particle shape characterisation and its application to discrete element modelling, Particuology, Volume 12, 2014, Pages 80 - 89, ISSN 1674 - 2001").

[0067] R c1 、R i1 、R c2 、R i2 The measurement methods of R i and R c are the same as those of R

[0068] R c3 and R i3 are measured by first preparing manganese dioxide into a slurry and then coating it on a substrate to form a film layer, and referring to the measurement methods of R i and R c for measurement. There are no special restrictions on the solid content of the slurry (such as 75wt%) and the type of substrate, as long as the purpose of this application can be achieved. R c4 and R i4 、R c5 and R i5 are measured with reference to the measurement methods of R c3 and R i3 .

[0069] Measurement of the areas of the first and second particles and calculation of their area percentages:

[0070] The software Image J was used to calculate the particle area. According to the recognized R c / R i ratio, it was determined whether the particle belonged to the first particle or the second particle. The sum of the particles with different attributions was recorded as the area of the first particle or the second particle. The percentage of the first particle area was the first particle area / image area × 100%, and the percentage of the second particle area was the second particle area / image area × 100%.

[0071] Measurement of the particle size of the positive electrode active material:

[0072] 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. After ultrasonic treatment for 30 min, it was added to the Malvern particle size analyzer to start the test. In the particle size distribution of the positive electrode active material on a volume basis, starting from the small particle size side, the particle size at which the volume cumulative reached 10% was the Dv10 of the positive electrode active material, the particle size at which the volume cumulative reached 50% was the Dv50 of the positive electrode active material, and the particle size at which the volume cumulative reached 90% was the Dv90 of the positive electrode active material.

[0073] Test of element content:

[0074] Based on the SEM image of the cross-section of the positive electrode sheet obtained above, the second particle was determined according to the particle size and area in the image, and then an energy dispersive spectrometer (EDS) was used for testing to determine the doping elements and element content;

[0075] The positive electrode material layer of the positive electrode sheet after cleaning with DMC was scraped off with a scraper, dissolved in a mixed solvent (for example, 10 ml of aqua regia (a mixture of nitric acid and hydrochloric acid in a volume ratio of 1:1) and 2 ml of HF were used for 0.4 g of positive electrode active material), and fixed volume to 100 mL. Then an inductively coupled plasma (ICP) analyzer was used to test the element content in the solution.

[0076] Test of the tap density of the positive electrode sheet:

[0077] Under the condition of 25 °C, the lithium-ion battery was charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C, and then discharged at a constant current of 1C to 2.8V. The lithium-ion battery was disassembled, and the positive electrode sheet was cleaned with DMC. After drying at 60 °C for 2 h, 5 pieces of positive electrode sheets with a size of 5 cm × 5 cm were cut. The thickness of the positive electrode sheet was measured respectively with a micrometer and recorded as d0 cm; the positive electrode material layer in the positive electrode sheet was scraped off with a scraper, the mass of the positive electrode material layer was weighed with a balance and recorded as m g, and the thickness of the positive electrode current collector after removing the positive electrode material layer was measured with a micrometer and recorded as d cm. The tap density of the positive electrode material layer was calculated according to the following formula:

[0078] The compaction density P = m / [25×(d0 - d)], with the unit g / cm 3 .

[0079] The compaction density of the positive electrode material layer is the average value of the compaction densities of the positive electrode material layers in the 5 positive electrode plates obtained by the above cutting.

[0080] Testing the particle size of the particles in the positive electrode material layer:

[0081] Under the condition of 25°C, charge the lithium-ion battery at a constant current of 0.5C to 4.2V, then charge it at a constant voltage of 4.2V to 0.05C, and then discharge it at a constant current of 1C to 2.8V. Disassemble the lithium-ion battery, and after burning the disassembled positive electrode plate or negative electrode plate into powder at 400°C in a vacuum, use a particle size analyzer to test the particle size to obtain the values of Dv10, Dv50, and Dv90.

[0082] Among them, Dv90 refers to the particle size that reaches 90% of the cumulative volume from the small particle size side in the particle size distribution based on volume; Dv50 refers to the particle size that reaches 50% of the cumulative volume from the small particle size side in the particle size distribution based on volume; Dv10 refers to the particle size that reaches 10% of the cumulative volume from the small particle size side in the particle size distribution based on volume.

[0083] Testing the rate performance and the cycle performance at 25°C:

[0084] (1) 2C room temperature rate performance and cycle performance at 25°C

[0085] Under the condition of 25°C, charge the lithium-ion battery at a constant current of 0.5C to 4.2V, then charge it at a constant voltage of 4.2V to 0.05C, and then discharge it at a constant current of 0.2C to 2.8V, and record the discharge capacity as D 01 ; Charge the lithium-ion battery at a constant current of 0.5C to 4.2V, then charge it at a constant voltage of 4.2V to 0.05C, and then discharge it at a constant current of 2C to 2.8V, and record the discharge capacity as D1. The 2C rate retention rate at 25°C (%) = D1 / D 01 ×100%.

[0086] According to the above operation steps, make the lithium-ion battery go through multiple "0.5C charge - 2C discharge" cycle processes, cycle 1000 times, and test the discharge capacity after the 1000th cycle as D 10 . The capacity retention rate after 1000 cycles at 25°C (%) = D 10 / D 01 ×100%.

[0087] (2) -10°C 1C low temperature rate performance

[0088] At 25°C, the lithium-ion battery is charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C, and then discharged at a constant current of 1C to 2.8V. Record the discharge capacity as D 02 ; At 25°C, the lithium-ion battery is charged at a constant current of 0.5C to 4.2V, then charged at a constant voltage of 4.2V to 0.05C. The temperature is adjusted to -10°C. After the battery cell is placed for 30 minutes, it is then discharged at a constant current of 1C to 2.8V. Record the discharge capacity as D2. The retention rate of the -10°C 1C rate (%) = D2 / D 02 × 100%.

[0089] Test of cycle performance:

[0090] Retention rate of cycle capacity at 40°C for 500 cycles:

[0091] The lithium-ion battery is charged at a constant current of 0.5C to 4.2V at 40°C, then charged at a constant voltage until the current is 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.8V. This is one charge-discharge cycle, and record the discharge capacity as D 03 ; According to the above operation steps, the lithium-ion battery is cycled 500 times. Test the discharge capacity after the 500th cycle as D3. The retention rate of capacity after 500 cycles at 40°C (%) = D3 / D 03 × 100%.

[0092] Test of manganese content in the negative electrode sheet:

[0093] Disassemble the lithium-ion battery that has been fully discharged after 500 cycles at 40°C. Take the negative electrode sheet and wash it with DMC, then dry it at 60°C for 2 hours. Then scrape off the negative electrode material layer of the negative electrode sheet, dissolve it with a mixed solvent (for example, 10 ml of aqua regia (a mixture of nitric acid and hydrochloric acid in a volume ratio of 1:1) is used for 0.4 g of negative electrode active material), make up the volume to 100 ml, and then use an ICP analyzer to test the manganese element content in the solution.

[0094] Example 1-1

[0095] <Preparation of the positive electrode sheet>

[0096] Weigh 203.3 kg of lithium carbonate (the mass percentage of lithium element is 18.71%), R c3 / R i31000 kg of manganese dioxide with an average value of 2.9 and a Dv50 of 17.2 μm (where the mass percentage of Mn element is 60.22%) and 56.2 kg of aluminum oxide (Al2O3, with a mass percentage of aluminum element of 52.91%) containing M2 metal element are mixed in a high-speed mixer at a rotation speed of 300 r / min for 20 min to obtain a mixture. The mixture is placed in an air furnace, heated to 790 °C at a rate of 5 °C / min, held for 24 h, taken out after natural cooling, and passed through a 300-mesh sieve to obtain a manganese-containing composite metal oxide, which is LMO. Among them, R c3 is the radius of the minimum circumscribed circle of the contour of the manganese dioxide particles, R i3 is the radius of the maximum inscribed circle of the contour of the manganese dioxide particles.

[0097] The positive electrode active material LMO, conductive agent Super P, and binder polyvinylidene fluoride are mixed according to a mass ratio of 96:2.4:1.6, N-methylpyrrolidone (NMP) is added, and the mixture is stirred in a vacuum mixer until the system becomes homogeneous to obtain a positive electrode slurry, where the solid content of the positive electrode slurry is 75 wt%. The positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and the aluminum foil is dried at 85 °C to obtain a positive electrode plate with a single-sided coating of the positive electrode material layer and a coating thickness of 110 μm. The above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode plate with a double-sided coating of the positive electrode material layer. Then, after cold pressing, slicing, and slitting, it is dried under vacuum conditions at 85 °C for 4 h to obtain a positive electrode plate with a specification of 74 mm × 867 mm. Among them, the R c / R i has an average value of 2.9 and a Dv50 of 17.9 μm.

[0098] <Preparation of negative electrode plate>

[0099] The negative electrode active material artificial graphite, conductive agent Super P, thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) are mixed according to a mass ratio of 96.4:1.5:0.5:1.6, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum mixer, where the solid content of the negative electrode slurry is 70 wt%. The negative electrode slurry is uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, and the copper foil is dried at 85 °C to obtain a negative electrode plate with a single-sided coating of the negative electrode material layer and a coating thickness of 130 μm. The above steps are repeated on the other surface of the aluminum foil to obtain a negative electrode plate with a double-sided coating of the negative electrode material layer. Then, after cold pressing, slicing, and slitting, it is dried under vacuum conditions at 120 °C for 12 h to obtain a negative electrode plate with a specification of 79 mm × 972 mm.

[0100] <Preparation of electrolyte>

[0101] In an argon atmosphere glove box with a water content of < 10 ppm, the chain carbonate DEC and the cyclic carbonate EC were mixed in a mass ratio of 57.5:30 to obtain a base solvent, and then the lithium salt LiPF6 was added to the base solvent and dissolved and mixed evenly. Among them, based on the mass of the electrolyte, the mass percentage content of LiPF6 was 12.5%, and the rest was the base solvent.

[0102] <Preparation of separator>

[0103] 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 slurry with a solid content of 50 wt%. The coating slurry was evenly coated on one surface of a 5-μm-thick PE film (provided by Celgard), dried at 85 °C to obtain a separator with a 5-μm-thick coating on one side. The above steps were repeated on the other surface of the separator to obtain a separator with a double-sided coated coating. Then, after drying and cold pressing, the separator was obtained. Among them, the porosity of the separator was 39%.

[0104] <Preparation of lithium-ion battery>

[0105] The positive electrode plate, separator, and negative electrode plate prepared above were stacked in sequence, with the separator placed in the middle of the positive electrode plate and the negative electrode plate to play a role in isolation, and wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum-plastic film packaging bag, dried and then injected with electrolyte, and a lithium-ion battery was obtained through processes such as vacuum packaging, standing, formation, degassing, and trimming. Among them, the formation conditions were constant current charging at 0.02C to 3.3V, and then constant current charging at 0.1C to 3.6V.

[0106] Examples 1-2 to 1-4

[0107] Except for adjusting the average value of R c3 / R i3 and Dv50 of manganese dioxide so that the average value of R c / R i of the positive electrode active material was as shown in Table 1, the rest was the same as Example 1-1.

[0108] Examples 1-5 and 1-6

[0109] Except that manganese dioxide in the raw materials was replaced with manganese tetroxide when preparing LMO, and the average value of R c4 / R i4 and Dv50 of manganese tetroxide were adjusted so that the average value of R c / R iExcept for the average value and Dv50 as shown in Table 1, the rest is the same as that of Example 1-1. Among them, R c4 is the radius of the minimum circumscribed circle of the contour of the manganese tetraoxide particles, and R i4 is the radius of the maximum inscribed circle of the contour of the manganese tetraoxide particles.

[0110] Example 2-1

[0111] Except in the <Preparation of the positive electrode sheet>, the positive electrode active material LMO, the positive electrode active material LiNi 0.55 Co 0.15 Mn 0.3 O2 (NCM5515), the conductive agent Super P, and the binder polyvinylidene fluoride are mixed according to a mass ratio of 76.8:19.2:2.4:1.6, NMP is added, and the mixture is stirred in a vacuum mixer until the system becomes homogeneous to obtain a positive electrode slurry with a solid content of 75 wt%, and the average value of R c3 / R i3 and Dv50 of manganese dioxide are adjusted so that the average value of R c / R i of the second particles and the Dv50 of the positive electrode active material are as shown in Table 2. Except for this, the rest is the same as that of Example 1-1.

[0112] The above NCM5515 is prepared by the following method: Lithium carbonate (where the mass percentage of lithium element is 18.71%), and R c5 / R i5 with an average value of 1.2 and a Dv50 of 16.3 μm of Ni 0.55 Co 0.15 Mn 0.3 (OH)2 precursor are mixed in a high-speed mixer at a rotation speed of 300 r / min for 20 min according to the ratio of the number of moles of Li to the number of moles of transition metal elements (the sum of the number of moles of Ni, Co, and Mn) of 1.05:0.997 to obtain a mixture. The mixture is placed in an oxygen kiln, heated to 890 °C at a rate of 5 °C / min, held for 12 h, taken out after natural cooling, and sieved through a 300-mesh sieve to obtain lithium nickel cobalt manganate, which is NCM5515. Among them, R c5 is the radius of the minimum circumscribed circle of the contour of the Ni 0.55 Co 0.15 Mn 0.3 (OH)2 precursor particles, and R i5 is the radius of the maximum inscribed circle of the contour of the Ni 0.55 Co 0.15 Mn 0.3 (OH)2 precursor particles.

[0113] Examples 2-2 to 2-4, Example 2-7

[0114] Except for mixing the corresponding cathode active materials according to Table 2 and adjusting the average value of R c3 / R i3 and Dv50 of manganese dioxide, and / or, Ni 0.55 Co 0.15 Mn 0.3 (OH)2 precursor's R c5 / R i5 average value and Dv50, the obtained R c1 / R i1 average value, R c2 / R i2 average value, the area percentage of the first particles, the area percentage of the second particles, the Dv50 of the cathode active material and the value of the particle size distribution (Dv90 - Dv10) / Dv50 of the cathode active material are shown in Table 2, and the rest is the same as in Example 2-1. Among them, NCM6010 in Table 2 is LiNi 0.6 Co 0.1 Mn 0.3 O2, NCM8309 is LiNi 0.83 Co 0.09 Mn 0.08 O2; by adjusting the ratio of the molar number of Li to the molar number of transition metal elements when preparing NCM5515, NCM6010 and NCM8309 satisfy the above chemical formula.

[0115] Examples 2-5 and 2-6

[0116] Except that when preparing the first particle LMO, manganese dioxide in the raw materials is replaced by manganese tetraoxide, and the R c4 / R i4 average value and Dv50 are adjusted, and when preparing the second particle LMO, the R c3 / R i3 average value and Dv50 are adjusted, the obtained R c1 / R i1 average value, R c2 / R i2 average value, the area percentage of the first particles, the area percentage of the second particles, the Dv50 of the cathode active material and the value of the particle size distribution (Dv90 - Dv10) / Dv50 of the cathode active material are shown in Table 2, and the rest is the same as in Example 2-1.

[0117] Examples 3-1 to 3-7

[0118] Except for obtaining the base solvent by adjusting the types and contents of chain carbonates and cyclic carbonates according to Table 3, the rest is the same as in Example 2-1.

[0119] Examples 4-1 to 4-9

[0120] Except that in <Preparation of electrolyte>, a sulfonate compound is further added to the electrolyte, and the type and mass percentage content of the sulfonate compound are adjusted according to Table 4, the rest is the same as Example 2-1.

[0121] Examples 5-1 to 5-6

[0122] Except that in the process of preparing LMO, a compound containing metal element M2 is added according to Table 5 and its content is adjusted so that the mass percentage content of metal element M2 is as shown in Table 5, the rest is the same as Example 2-1.

[0123] Example 5-7

[0124] Except that commercial LiFePO4 with a Dv50 of 1.0 μm (denoted as LFP) is used to replace NCM5515, the rest is the same as Example 5-3.

[0125] Example 5-8

[0126] Except that commercial LiMn 0.75 Fe 0.25 PO4 (denoted as LMFP) is used to replace NCM5515, the rest is the same as Example 5-3.

[0127] Example 5-9

[0128] Except that commercial LFP with a Dv50 of 1.0 μm is used to replace part of NCM5515 so that the mass ratio of LMO, NCM5515, LFP, Super P, and polyvinylidene fluoride is 76.8:9.2:10:2.4:1.6, the rest is the same as Example 5-3.

[0129] Comparative Example 1

[0130] Except that the average value of R c / R i and the Dv50 of the positive electrode active material are as shown in Table 1, the rest is the same as Example 1-1.

[0131] The preparation parameters and performance tests of each example and comparative example are shown in Tables 1 to 5.

[0132] Table 1

[0133]

[0134]

[0135] It can be seen from Examples 1-1 to 1-6 and Comparative Example 1 that when the value of R c / R i is within the scope of the present application, the obtained lithium-ion battery has good low-temperature rate performance and room-temperature rate performance.

[0136] Table 2

[0137]

[0138] 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 usually affect the performance of the lithium-ion battery. It can be seen from Examples 2-1 to 2-7 that 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 scope of the present application, the obtained lithium-ion battery has good low-temperature rate performance and room-temperature rate performance.

[0139] Table 3

[0140]

[0141]

[0142] The types and mass percentage contents of the linear carbonate and cyclic carbonate in the electrolyte, and the value of ω1 / ω2 usually affect the performance of the lithium-ion battery. It can be seen from Example 2-1, Examples 3-1 to 3-7 that when the types and mass percentage contents of the linear carbonate and cyclic carbonate, and the value of ω1 / ω2 are within the scope of the present application, the obtained lithium-ion battery has good low-temperature rate performance.

[0143] Table 4

[0144]

[0145] Note: " / " in Table 4 indicates the absence of corresponding preparation parameters or substances.

[0146] It can be seen from Example 2-1, Examples 4-1 to 4-9 that adding a sulfonate compound to the electrolyte can improve the cycling performance of the lithium-ion battery at high temperature and the manganese dissolution phenomenon on the negative electrode sheet. It can be seen from Examples 4-1 to 4-9 that when the types and mass percentage contents of the sulfonate compound are within the scope of the present application, the obtained lithium-ion battery has good high-temperature cycling performance and less manganese dissolution on the negative electrode sheet. Also, when the value of A / B is within the scope of the present application, the obtained lithium-ion battery has good high-temperature cycling performance and less manganese dissolution on the negative electrode sheet.

[0147] Table 5

[0148]

[0149] The types of elements in the positive electrode active material usually affect the performance of the lithium-ion battery. It can be seen from Examples 2-1, 5-1 to 5-9 that when the positive electrode active material includes Mn and metal element M1, the obtained lithium-ion battery has good low-temperature rate performance. In addition, it can also be seen that when the second particle contains metal element M2 and its type and mass percentage content are within the scope of this application, the obtained lithium-ion battery has good low-temperature rate performance.

[0150] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application shall be included within the scope of protection of this application.

Claims

1. An electrochemical device, which includes a positive electrode plate and an electrolyte, The positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, and in a scanning electron microscope photograph of the cross-section of the positive electrode material layer, the radius of the minimum circumscribed circle of the contour of the positive electrode active material particles with an area greater than 5 μm 2 is R c , and the radius of the maximum inscribed circle of the contour of the positive electrode active material particles with an area greater than 5 μm 2 is R i , satisfying 1 < R c / R i and the average value ≤ 3; The electrolyte includes a chain carbonate and a cyclic carbonate. Based on the mass of the electrolyte, the mass percentage of the chain carbonate is ω1, and the mass percentage ω2 of the cyclic carbonate is 25% to 50%, satisfying ω1 / ω2 is 0.75 to 2.

5.

2. The electrochemical device according to claim 1, wherein, The area is greater than 5 μm 2 The positive electrode active material particles include first particles and second particles. The radius of the minimum circumscribed circle of the contour of the first particles is R c1 and the radius of the maximum inscribed circle of the contour of the first particles is R i1 satisfying 1 < R c1 / R i1 The average value of ≤ 1.5; the radius of the minimum circumscribed circle of the contour of the second particles is R c2 and the radius of the maximum inscribed circle of the contour of the second particles is R i2 satisfying 1.5 < R c2 / R i2 The average value of ≤ 3.

3. The electrochemical device according to claim 2, which satisfies: Based on the cross-sectional area of the positive electrode material layer, the area percentage of the first particles is greater than 0% and less than or equal to 50%, and the area percentage B of the second particles is 30% to 80%; and / or, The average cross-sectional area of the first particles is smaller than the average cross-sectional area of the second particles.

4. The electrochemical device according to claim 1, wherein, Meet at least one of the conditions (a) to (b): (a) The positive electrode active material includes lithium manganate; (b) The positive electrode active material includes a composite metal oxide of lithium element and transition metal element, the transition metal element includes Mn and metal element M1, and the metal element M1 includes at least one of Ni, Co or Fe.

5. The electrochemical device according to claim 2, wherein, The second particle includes a metal element M2, and the metal element M2 includes at least one of Al, Mg or Nb.

6. The electrochemical device according to claim 2, wherein, The second particle includes a metal element M2, and based on the mass of the second particle, the mass percentage of the metal element M2 is 0.1% to 3%.

7. The electrochemical device according to claim 1, wherein the volume particle size distribution of the positive electrode active material satisfies at least one of conditions (c) to (d): (c) 9 μm ≤ Dv50 ≤ 22 μm; (d) 0.9 ≤ (Dv90 - Dv10) / Dv50 ≤ 2.

8. The electrochemical device according to claim 1, wherein, The chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate or dibutyl carbonate.

9. The electrochemical device according to claim 1, wherein, The cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate or butylene carbonate.

10. The electrochemical device according to claim 3 further comprises an electrolyte, the electrolyte comprising a sulfonate compound, and the mass percentage content of the sulfonate compound is A based on the mass of the electrolyte, satisfying 0.006 ≤ A / B ≤ 0.

1.

11. The electrochemical device according to claim 10, wherein 0.5％≤A≤10％。 12. The electrochemical device according to claim 10, wherein The sulfonate compound includes at least one of the following structural compounds I-1 to I-14:

13. The electrochemical device according to claim 1 further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode material layer, the negative electrode material layer comprising a negative electrode active material, and the negative electrode active material comprising at least one of artificial graphite, natural graphite or hard carbon.

14. An electronic device comprising the electrochemical device according to any one of claims 1 to 13.

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