Electrochemical device and electronic device comprising same

Abstract

The invention provides an electrochemical device and an electronic device comprising the same, the electrochemical device comprises a positive pole piece, the positive pole piece comprises a current collector and a positive pole material layer located on at least one surface of the current collector in the thickness direction, the positive pole material layer comprises a first positive pole material layer and a second positive pole material layer, the second positive electrode material layer is located between the first positive electrode material layer and the current collector, the positive electrode material layer comprises a positive electrode active material, the positive electrode active material comprises two or more than two nickel cobalt lithium manganate ternary materials, the two or more than two nickel cobalt lithium manganate ternary materials are divided into two groups, the chemical formula of the first group of lithium nickel cobalt manganate ternary materials is Lin1Nix1Coy1Mnz1M1m1O2, x1 + y1 + z1 + m1 is equal to 1 and smaller than or equal to 0.60, the chemical formula of the second group of lithium nickel cobalt manganate ternary materials is Lin2Nix2Coy2Mnz2M2m2O2, x2 + y2 + z2 + m2 is equal to 1 and larger than 0 and smaller than or equal to 0.14, and the two groups of lithium nickel cobalt manganate ternary materials are located in the first positive electrode material layer and the second positive electrode material layer respectively.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device comprising the same. Background Technology

[0002] The positive electrode active materials for lithium-ion batteries include ternary materials such as lithium nickel cobalt manganese oxide (NCM) and lithium cobalt oxide. Lithium batteries using NCM as the positive electrode active material have the advantages of low cost, high specific capacity, and good safety.

[0003] However, currently, NCM lithium batteries quickly reach the discharge cutoff voltage (3.0V) when discharging at low temperature and low state of charge (SOC), making it difficult to meet the requirements of practical product applications. Lithium batteries using lithium cobalt oxide as the cathode material can achieve low temperature and low SOC discharge to meet the requirements, but lithium cobalt oxide materials require the consumption of cobalt metal resources, which are relatively scarce, resulting in higher costs and hindering cost reduction. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device comprising the same, to improve the discharge performance of NCM lithium batteries under low temperature and low SOC conditions. The specific technical solution is as follows:

[0005] The first aspect of this application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a current collector and a positive electrode material layer located on at least one surface of the current collector in the thickness direction, the positive electrode material layer comprising a first positive electrode material layer and a second positive electrode material layer, the second positive electrode material layer being located between the first positive electrode material layer and the current collector, the positive electrode material layer comprising a positive electrode active material, the positive electrode active material comprising two or more lithium nickel cobalt manganese oxide ternary materials, wherein the two or more lithium nickel cobalt manganese oxide ternary materials are divided into two groups, the first group of lithium nickel cobalt manganese oxide ternary materials having the chemical formula Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, preferably 0.15≤y1≤0.45, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, preferably 0<y2≤0.08, with two sets of nickel-cobalt-manganese ternary materials located in the first and second cathode material layers, respectively. By controlling the structure of the cathode material layers and the type and content of the cathode active materials, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0006] In one embodiment of this application, the lithium nickel cobalt manganese oxide ternary material may include doping or coating elements, and the materials M1 and M2 are each independently selected from at least one of Ag, Sn, Zn, Al, Mo, Cu, B, Ti, and Fe. Adding the above-mentioned doping or coating elements to the positive electrode active material can make the conductive network on the surface of the positive electrode active material particles more compact and improve its kinetic performance; on the other hand, it can reduce the specific surface area of ​​the positive electrode active material, reducing side reactions between the positive electrode active material and the electrolyte; furthermore, it is beneficial to form a passivation film on the surface of the positive electrode active material particles, improving its first-efficiency and reversible capacity. It should be noted that Li... n1 Ni x1 Co y1 Mn z1 M1 m1 O2 and Li n2 Ni x2 Co y2 Mn z2 M2 m2 In O2, m1 and m2 can be 0, meaning that nickel-cobalt-manganese ternary materials may not include doped or coated elements.

[0007] In one embodiment of this application, a first group of lithium nickel cobalt manganese oxide (LCO) ternary materials is located in a first cathode material layer, and a second group of LCO ternary materials is located in a second cathode material layer. Based on the total mass of the LCO ternary materials, the mass percentage of the first group of LCO ternary materials is a1, and the mass percentage of the second group of LCO ternary materials is b1, satisfying 5% ≤ a1 ≤ 70%, 30% ≤ b1 ≤ 95%, preferably 25% ≤ a1 ≤ 65%, 35% ≤ b1 ≤ 75%, and more preferably 40% ≤ a1 ≤ 60%, 40% ≤ b1 ≤ 60%. By controlling the types of materials in the cathode material layer and the content of LCO ternary materials with different cobalt contents within the scope of this application, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0008] In one embodiment of this application, the second group of lithium nickel cobalt manganese oxide ternary materials is located in the first cathode material layer, and the first group of lithium nickel cobalt manganese oxide ternary materials is located in the second cathode material layer. Based on the total mass of the lithium nickel cobalt manganese oxide ternary materials, the mass percentage of the first group of lithium nickel cobalt manganese oxide ternary materials is a2, and the mass percentage of the second group of lithium nickel cobalt manganese oxide ternary materials is b2, satisfying 25%≤a2≤95%, 5%≤b2≤75%, preferably 35%≤a2≤80%, 20%≤b2≤65%, and more preferably 45%≤a2≤65%, 35%≤b2≤55%. By controlling the types of materials in the cathode material layer and the content of lithium nickel cobalt manganese oxide ternary materials with different cobalt contents within the scope of this application, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0009] In one embodiment of this application, the coating weight of the positive electrode material layer is 6 mg / cm³. 2 Up to 11 mg / cm 2 By adjusting the coating weight of the cathode material layer within the scope of this application, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0010] In one embodiment of this application, the particle size of the first group of lithium nickel cobalt manganese oxide ternary materials is D. V1 50, 1μm≤D V1 50≤10μm, preferably, 2μm≤D V1 50≤9μm. By controlling the particle size of lithium nickel cobalt manganese oxide ternary materials within the scope of this application, the lithium-ion transport distance during battery charging and discharging can be improved, thereby extending the battery's discharge time in low-temperature environments.

[0011] In one embodiment of this application, the particle size of the second group of lithium nickel cobalt manganese oxide ternary materials is D. V2 50, 1μm≤D V2 50≤15μm, optionally, 2μm≤D V2 50≤10μm. By controlling the particle size of lithium nickel cobalt manganese oxide ternary materials within the range of this application, the lithium-ion transport distance during battery charging and discharging can be improved, thereby extending the battery's discharge time in low-temperature environments.

[0012] In one embodiment of this application, the first group of lithium nickel cobalt manganese oxide ternary materials has the chemical formula Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, where 0.95≤n1≤1.05, 0.3≤x1≤0.84, 0.01≤z1≤0.7, 0≤m1≤0.2; the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2Ni x2 Co y2 Mn z2 M2 m2 O2, where 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, and 0≤m2≤0.2.

[0013] In one embodiment of this application, the positive electrode active material includes two ternary nickel-cobalt-manganese oxide materials, NCM-1 and NCM-2. NCM-1 satisfies: 0.15 ≤ y1 ≤ 0.60, and NCM-2 satisfies: 0 < y2 ≤ 0.14. By controlling the range of cobalt content y in the ternary nickel-cobalt-manganese oxide materials within the scope of this application, it is preferable to use two ternary nickel-cobalt-manganese oxide materials. This can reduce battery impedance while increasing the battery discharge voltage platform, thereby improving the battery's discharge capability in low-temperature environments.

[0014] In one embodiment of this application, the mass percentage of lithium nickel cobalt manganese oxide ternary material is 90% to 98% based on the mass of the cathode material layer. By controlling the mass of the lithium nickel cobalt manganese oxide ternary material within the scope of this application, the energy density and stability of the battery can be improved, thereby enhancing the discharge performance of the lithium battery under low temperature and low SOC conditions.

[0015] In one embodiment of this application, the positive electrode material layer further includes a conductive agent and a binder. The conductive agent is made of at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The binder is made of at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, and potassium hydroxymethyl cellulose.

[0016] In one embodiment of this application, the mass percentage of the conductive agent is 1% to 8% and the mass percentage of the binder is 1% to 3%, based on the mass of the positive electrode material layer.

[0017] A second aspect of this application provides a method for preparing an electrochemical device according to any of the foregoing embodiments.

[0018] Preparation of positive electrode: Two groups of lithium nickel cobalt manganese oxide ternary materials were divided into two groups of positive electrode active materials. The chemical formula of the first group of lithium nickel cobalt manganese oxide ternary materials is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Nix2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, two sets of positive electrode active materials are respectively set in the first positive electrode material layer and the second positive electrode material layer to obtain the positive electrode sheet. By controlling the preparation method of the electrochemical device, the electrochemical device provided in this application can have good performance.

[0019] A third aspect of this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments.

[0020] The beneficial effects of this application are:

[0021] An electrochemical device includes a positive electrode, which comprises a current collector and a positive electrode material layer located on at least one surface of the current collector along its thickness direction. The positive electrode material layer includes a first positive electrode material layer and a second positive electrode material layer, with the second positive electrode material layer located between the first positive electrode material layer and the current collector. The positive electrode material layer includes a positive electrode active material, which comprises two or more lithium nickel cobalt manganese oxide ternary materials. The two or more lithium nickel cobalt manganese oxide ternary materials are divided into two groups, with the first group of lithium nickel cobalt manganese oxide ternary materials having the chemical formula Li. n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14; two sets of nickel-cobalt-manganese ternary materials are located in the first cathode material layer and the second cathode material layer, respectively. By controlling the structure of the cathode material layer and the type and content of the cathode active material, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0022] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following embodiments are provided to further illustrate this application in detail. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0024] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0025] This application provides an electrochemical device, including a positive electrode sheet. The positive electrode sheet includes a current collector and a positive electrode material layer located on at least one surface of the current collector in the thickness direction. The positive electrode material layer includes a first positive electrode material layer and a second positive electrode material layer, with the second positive electrode material layer located between the first positive electrode material layer and the current collector. The positive electrode material layer includes a positive electrode active material, which includes two or more lithium nickel cobalt manganese oxide ternary materials. The two or more lithium nickel cobalt manganese oxide ternary materials are divided into two groups, with the first group of lithium nickel cobalt manganese oxide ternary materials having the chemical formula Li. n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, preferably 0.15≤y1≤0.45, 0<y2≤0.08. For example, y1 can be 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, or any range of two of the above values; y2 can be 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, or any range of two of the above values. Two sets of lithium nickel cobalt manganese oxide ternary materials are respectively located in the first cathode material layer and the second cathode material layer.

[0026] The inventors discovered that when lithium nickel cobalt manganese oxide (LCO) is used as the positive electrode active material, it quickly reaches the discharge cutoff voltage (3.0V) under low-temperature, low-SOC discharge conditions, making its low-temperature, low-SOC discharge performance unsatisfactory for practical product applications. While lithium cobalt oxide is typically used as a substitute for LCO to achieve satisfactory discharge performance under low-temperature, low-SOC conditions, it requires the use of cobalt metal resources, which are relatively scarce, resulting in higher costs and hindering cost reduction. When the cobalt content in a lithium nickel cobalt manganese oxide ternary material is high (e.g., 0.15 ≤ y ≤ 0.60), the discharge voltage is lower and the discharge curve is flatter. Conversely, when the cobalt content is low (e.g., 0 < y ≤ 0.14), the discharge voltage is higher and the slope of the discharge curve is steeper. Two or more lithium nickel cobalt manganese oxide ternary materials meeting these ranges are divided into two groups. During the preparation of the cathode material, the two groups of cathode active materials are double-coated onto the cathode electrode sheet. This allows the cathode electrode sheet to simultaneously possess the characteristics of high discharge voltage and a flat discharge curve, thereby improving low-temperature discharge capability. Increasing the cobalt content in the ternary material can reduce the battery impedance and lower the discharge voltage plateau. Lower impedance helps extend the low-temperature discharge time of the battery, but lower discharge voltage shortens the low-temperature discharge time. Therefore, the cobalt content can be within a relatively optimal range based on experimental results.

[0027] In one embodiment of this application, the lithium nickel cobalt manganese oxide ternary material may include doping or coating elements, and the materials M1 and M2 are each independently selected from at least one of Ag, Sn, Zn, Al, Mo, Cu, B, Ti, and Fe. Adding the above-mentioned doping or coating elements to the positive electrode active material can make the conductive network on the surface of the positive electrode active material particles more compact and improve its kinetic performance; on the other hand, it can reduce the specific surface area of ​​the positive electrode active material, reducing side reactions between the positive electrode active material and the electrolyte; furthermore, it is beneficial to form a passivation film on the surface of the positive electrode active material particles, improving its first-efficiency and reversible capacity. It should be noted that Li... n1 Ni x1 Co y1 Mn z1 M1 m1 O2 and Li n2 Ni x2 Co y2 Mn z2 M2 m2 In O2, m1 and m2 can be 0, meaning that nickel-cobalt-manganese ternary materials may not include doped or coated elements.

[0028] In one embodiment of this application, a first group of lithium nickel cobalt manganese oxide ternary materials is located in a first cathode material layer, and a second group of lithium nickel cobalt manganese oxide ternary materials is located in a second cathode material layer. Based on the total mass of the lithium nickel cobalt manganese oxide ternary materials, the mass percentage of the first group of lithium nickel cobalt manganese oxide ternary materials is a1, and the mass percentage of the second group of lithium nickel cobalt manganese oxide ternary materials is b1, wherein 5%≤a1≤70%, 30%≤b1≤95%, preferably 25%≤a1≤65%, 35%≤b1≤75%, and more preferably 40%≤a1≤60%, 40%≤b1≤60%. For example, a1 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range of any two of the above values, and b1 can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range of any two of the above values. By adjusting the type of material in the positive electrode layer and the content of different cobalt contents of the nickel-cobalt-manganese ternary material within the scope of this application, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0029] In one embodiment of this application, the second group of lithium nickel cobalt manganese oxide ternary materials is located in the first cathode material layer, and the first group of lithium nickel cobalt manganese oxide ternary materials is located in the second cathode material layer. Based on the total mass of the lithium nickel cobalt manganese oxide ternary materials, the mass percentage of the first group of lithium nickel cobalt manganese oxide ternary materials is a2, and the mass percentage of the second group of lithium nickel cobalt manganese oxide ternary materials is b2, satisfying 25%≤a2≤95%, 5%≤b2≤75%, preferably 35%≤a2≤80%, 20%≤b2≤65%, and more preferably 45%≤a2≤65%, 35%≤b2≤55%. For example, a2 can be 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range of any two of the above values, and b2 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or a range of any two of the above values. By adjusting the type of material in the positive electrode layer and the content of different cobalt contents of the nickel-cobalt-manganese ternary material within the scope of this application, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0030] In one embodiment of this application, the coating weight of the positive electrode material layer is 6 mg / cm³. 2 Up to 11 mg / cm 2By adjusting the coating weight of the cathode material layer within the scope of this application, the accuracy and uniformity of the coating layer density can be improved, thereby enhancing the energy density, cycle stability, and safety of the battery.

[0031] In one embodiment of this application, the particle size of the first group of lithium nickel cobalt manganese oxide ternary materials is D. V1 50, 1μm≤D V1 50≤10μm, preferably, 2μm≤D V1 50≤9μm, for example, D V1 50 can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or a range of any two of the above values. The particle size of the second group of lithium nickel cobalt manganese oxide ternary materials is D. V2 50, 1μm≤D V2 50≤15μm, preferably, 2μm≤D V2 50≤10μm, for example, D V2 The particle size 50 can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, or a range of any two of the above values. The particle size of the lithium nickel cobalt manganese oxide ternary material affects the lithium-ion transport distance during battery charging and discharging. A larger transport distance reduces the discharge time at low temperatures. By controlling the particle size of the lithium nickel cobalt manganese oxide ternary material within the range of this application, the lithium-ion transport distance during battery charging and discharging can be improved, thereby extending the battery's discharge time in low-temperature environments.

[0032] In one embodiment of this application, the first group of lithium nickel cobalt manganese oxide ternary materials has the chemical formula Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, where 0.95≤n1≤1.05, 0.3≤x1≤0.84, 0.01≤z1≤0.7, 0≤m1≤0.2; the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2O2, where 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, and 0≤m2≤0.2.

[0033] In one embodiment of this application, the positive electrode active material includes two types of lithium nickel cobalt manganese oxide ternary materials, grouped according to the cobalt content y, into NCM-1 and NCM-2. NCM-1 satisfies: 0.15 ≤ y1 ≤ 0.60. For example, y1 can be 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, or any range of two of the above values. NCM-2 satisfies: 0 < y2 ≤ 0.14. For example, y2 can be 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, or any range of two of the above values. By controlling the range of cobalt content y in the lithium nickel cobalt manganese oxide ternary materials within the scope of this application, it is preferable to use two types of lithium nickel cobalt manganese oxide ternary materials. This can reduce battery impedance while increasing the battery discharge voltage platform, thereby improving the battery's discharge capability in low-temperature environments and simplifying the production process.

[0034] In one embodiment of this application, the mass percentage of lithium nickel cobalt manganese oxide ternary material is 90% to 98% based on the mass of the cathode material layer. Exemplarily, the mass percentage of lithium nickel cobalt manganese oxide ternary material can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or a range consisting of any two of the above values. By controlling the content of lithium nickel cobalt manganese oxide ternary material within the above range, the discharge performance of NCM lithium batteries under low temperature and low SOC conditions can be improved.

[0035] In this application, there are no particular limitations on the preparation method of the lithium nickel cobalt manganese oxide ternary material, as long as it can achieve the purpose of this invention. For example, the following methods can be used for preparation:

[0036] Ni, Co, and Mn nitrates, sulfates, or chlorides are co-precipitated in the presence of ammonia or ammonium bicarbonate complexing agents to prepare NCM carbonate or hydroxide precursors. The precursors are then sintered with lithium hydroxide or lithium carbonate at 700°C to 1000°C to obtain lithium nickel cobalt manganese oxide ternary materials.

[0037] In this application, the positive electrode material layer further includes a conductive agent and a binder. The conductive agent is selected from at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. Exemplarily, the conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black, and the carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The binder is selected from at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0038] In one embodiment of this application, based on the mass of the positive electrode material layer, the mass percentage content of the conductive agent is 1% to 8%. Exemplarily, the mass percentage content of the conductive agent can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any combination of the above values. The mass percentage content of the binder is 1% to 3%. Exemplarily, the mass percentage content of the binder can be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or any combination of the above values. By controlling the type and content of the conductive agent and binder within the above ranges, the discharge performance of the NCM lithium battery under low temperature and low SOC conditions can be improved.

[0039] The positive electrode sheet of this application also includes a positive current collector. This application does not have any particular restrictions on the positive current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil or composite current collector (e.g., aluminum-carbon composite current collector).

[0040] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the positive electrode material layer can be 30 μm to 120 μm.

[0041] In this application, the electrochemical device further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0042] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0043] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0044] In some embodiments of this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0045] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0046] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0047] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0048] In this application, the electrochemical device also includes a diaphragm. This application does not impose any particular limitation on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0049] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. 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.

[0050] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0051] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, 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, or barium sulfate. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0052] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 3 μm to 30 μm.

[0053] A second aspect of this application provides a method for preparing the electrochemical device according to any of the foregoing embodiments. Two sets of lithium nickel cobalt manganese oxide ternary materials are used as two sets of positive electrode active materials, wherein the chemical formula of the first set of lithium nickel cobalt manganese oxide ternary materials is Li… n1 Ni x1 Co y1 Mn z1 M1 m1O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, two sets of positive electrode active materials are respectively set in the first positive electrode material layer and the second positive electrode material layer to obtain the positive electrode sheet.

[0054] A third aspect of this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments. The electronic device provided by this application has good performance. This application does not particularly limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0055] Example

[0056] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0057] Test methods and equipment:

[0058] Cobalt content test:

[0059] Using scanning electron microscopy (SEM), NCM material particles were selected, and elemental analysis was performed on the selected NCM particles using energy dispersive spectroscopy (EDS). It should be noted that the EDS measurement yields the mass of each element. To obtain the molar mass of each element's atoms, the following formula needs to be used: n' = m' / M', where n' is the molar mass of each element's atoms, m' is the mass of each element measured by EDS, and M' is the molar mass of each element. Therefore, the molar mass of cobalt atoms in the lithium nickel cobalt manganese oxide ternary material is n'(Co) = m'(Co) / M'(Co).

[0060] Tests on the content of each component in the cathode material layer:

[0061] The prepared positive electrode sheet was calcined at 500℃ for 4 hours under oxygen-permeable conditions to remove carbon conductive agent and organic binder components. The powder after high-temperature treatment was evenly dispersed in water, and 1 mL of suspension was dried to prepare a sample. SEM and EDS were used for observation at 1000x magnification. The composition and number of all NCM particles in the random field of view were counted, and the content of each component was counted based on the composition and number of particles.

[0062] Particle size testing:

[0063] After drying the above suspension and preparing samples, when using SEM and EDS for observation, in addition to statistically analyzing the composition and particle number, the particle size should also be statistically analyzed to obtain the D of different components. V 50.

[0064] Low-temperature discharge performance test

[0065] The battery was subjected to a low temperature and low SOC discharge test: the battery was discharged to 3.0V at a discharge rate of 0.2C, and then charged at a rate of 0.2C for 0.5H. The battery was placed at a low temperature of 0℃ and discharged at a rate of 1C and 0.5C respectively. The duration of discharge to 3.0V was recorded.

[0066] Example 1-1

[0067] <Preparation of the positive electrode>

[0068] LiNi 0.5 Co 0.4 Mn 0.09 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNT, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred evenly to obtain the first positive electrode slurry. LiNi 0.5 Co 0.05 Mn 0.44 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNT, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred evenly to obtain a second positive electrode slurry. The first positive electrode slurry was deposited on a first positive electrode material layer, and the second positive electrode slurry was deposited on a second positive electrode material layer. The first and second positive electrode material layers were coated on one surface of a 10 μm thick positive electrode current collector aluminum foil at a ratio of 40%:60%. The coating weight of the positive electrode material layer on the positive electrode sheet was 8 mg / cm³.2 The aluminum foil is dried at 90℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After coating, the positive electrode sheet is cold-pressed to a compaction density of 4.1 g / cm³. 3 After cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for later use.

[0069] <Preparation of Negative Electrode Sheets>

[0070] Artificial graphite, conductive carbon black (Super P), and polyacrylic acid, the negative electrode active materials, were mixed in a weight ratio of 97.3:1.5:1.2. Deionized water (H2O) was added as a solvent to prepare a slurry with a solid content of 70 wt%, and the mixture was stirred evenly to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 10 μm thick copper foil for the negative electrode current collector. The coating weight of the negative electrode material layer on the negative electrode sheet was 95 g / m². 2 The copper foil is dried at 110℃ to obtain a negative electrode sheet with a single-sided coating of negative electrode material. The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After coating, the negative electrode sheet is cold-pressed to a compaction density of 1.7 g / cm³. 3 After cutting and welding the tabs, a negative electrode sheet with dimensions of 78mm × 875mm is obtained for later use. The artificial graphite used as the negative electrode active material has a Dv50 of 10μm and a specific surface area of ​​1.6m² achieved by adjusting the ball milling time. 2 / g.

[0071] <Preparation of Electrolyte>

[0072] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly at a mass ratio of EC:EMC:DEC = 3:5:2 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6) was added to the base solvent and mixed uniformly to obtain an electrolyte. The lithium salt content was 12.5% ​​by mass, with the remainder being the base solvent.

[0073] <Septum>

[0074] A polyethylene film with a thickness of 9μm was selected as the diaphragm.

[0075] <Preparation of Lithium-ion Batteries>

[0076] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in an outer packaging foil and then injected with the prepared electrolyte. After formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0077] Examples 1-2 to Examples 1-40

[0078] Except for changing the preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0079] Examples 1-41

[0080] LiNi with a mass ratio of 1:1 0.5 Co 0.4 Mn 0.09 Al 0.01 O2 and LiNi 0.4 Co 0.5 Mn 0.09 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNTs, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5. N-methylpyrrolidone (NMP) was then added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred until homogeneous to obtain the first positive electrode slurry. LiNi was then... 0.5 Co 0.05 Mn 0.44 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNT, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred until homogeneous to obtain a second positive electrode slurry. The first positive electrode slurry was deposited on a first positive electrode material layer, and the second positive electrode slurry was deposited on a second positive electrode material layer. The first and second positive electrode material layers were coated onto one surface of a 10 μm thick aluminum foil at a ratio of 40%:60%. The coating weight of the positive electrode material layer on the positive electrode sheet was 8 mg / cm³. 2 The aluminum foil is dried at 90℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After coating, the positive electrode sheet is cold-pressed to a compaction density of 4.1 g / cm³. 3 After cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for later use.

[0081] Examples 1-42

[0082] LiNi0.5 Co 0.4 Mn 0.09 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNTs, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred until homogeneous to obtain the first positive electrode slurry. LiNi was then added in a 1:1 mass ratio. 0.5 Co 0.05 Mn 0.44 Al 0.01 O2 and LiNi 0.5 Co 0.1 Mn 0.39 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNT, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred until homogeneous to obtain a second positive electrode slurry. The first positive electrode slurry was deposited on a first positive electrode material layer, and the second positive electrode slurry was deposited on a second positive electrode material layer. The first and second positive electrode material layers were coated onto one surface of a 10 μm thick aluminum foil at a ratio of 40%:60%. The coating weight of the positive electrode material layer on the positive electrode sheet was 8 mg / cm³. 2 The aluminum foil is dried at 90℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After coating, the positive electrode sheet is cold-pressed to a compaction density of 4.1 g / cm³. 3 After cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for later use.

[0083] Examples 1-43

[0084] LiNi with a mass ratio of 1:1 0.5 Co 0.4 Mn 0.09 Al 0.01 O2 and LiNi 0.4 Co 0.5 Mn 0.09 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNTs, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred until homogeneous to obtain the first positive electrode slurry. LiNi was then added in a 1:1 mass ratio.0.5 Co 0.05 Mn 0.44 Al 0.01 O2 and LiNi 0.5 Co 0.1 Mn 0.39 Al 0.01 O2 was mixed with conductive carbon black (Super P), CNT, and polyvinylidene fluoride (PVDF) in a weight ratio of 96.5:1.0:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. The mixture was stirred until homogeneous to obtain a second positive electrode slurry. The first positive electrode slurry was deposited on a first positive electrode material layer, and the second positive electrode slurry was deposited on a second positive electrode material layer. The first and second positive electrode material layers were coated onto one surface of a 10 μm thick aluminum foil at a ratio of 40%:60%. The coating weight of the positive electrode material layer on the positive electrode sheet was 8 mg / cm³. 2 The aluminum foil is dried at 90℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After coating, the positive electrode sheet is cold-pressed to a compaction density of 4.1 g / cm³. 3 After cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for later use.

[0085] Comparative Examples 1 to 3

[0086] Except for changing the preparation parameters according to Table 1, the rest is the same as in Example 1-1.

[0087]

[0088]

[0089] Table 2

[0090] Group Discharge time at 0℃ and 0.5C 0℃ 1C discharge time Examples 1-41 6min45s 2min32s Examples 1-42 6min27s 2min15s Examples 1-43 6min43s 2 minutes 30 seconds

[0091] As can be seen from Examples 1-1 to 1-11 and Comparative Examples 1 to 3, by adjusting the cobalt content y1 and y2 in the two sets of lithium nickel cobalt manganese oxide ternary materials within the scope of this application, the discharge time of the secondary battery at 0°C and 1C and 0.5C rates was improved, indicating that the discharge performance of the lithium-ion battery at low temperature and low SOC was improved. Based on the discharge times of Examples 1-1 to 1-11 at 0°C and 1C and 0.5C rates, the cobalt content y1 and y2 have a preferred range.

[0092] Based on the total mass of the positive electrode active material, the mass percentage of the two sets of lithium nickel cobalt manganese oxide ternary materials affects the low-temperature discharge performance of the secondary battery. As can be seen from Examples 1-1, 1-12 to 1-16 and 1-37 and 1-38, when the first set of lithium nickel cobalt manganese oxide ternary materials is located in the first positive electrode material layer and the second set of lithium nickel cobalt manganese oxide ternary materials is located in the second positive electrode material layer, by adjusting the mass percentages a1 and b1 of the two sets of lithium nickel cobalt manganese oxide ternary materials in the first and second positive electrode material layers to satisfy 5%≤a1≤70% and 30%≤b1≤95%, the discharge time of the secondary battery at 0°C low temperature conditions at 1C and 0.5C rates is improved, thus indicating that the discharge performance of lithium-ion batteries at low temperature and low SOC conditions is improved. From Examples 1-12 to 1-16, it can be seen that the discharge time of the two groups of lithium nickel cobalt manganese oxide ternary materials first increases and then decreases as the mass percentage content a1 and b1 increases. This indicates that the mass percentage content a1 and b1 of the lithium nickel cobalt manganese oxide ternary materials have a preferred range: 25% ≤ a1 ≤ 65%, 35% ≤ b1 ≤ 75%. Further, 40% ≤ a1 ≤ 60%, 40% ≤ b1 ≤ 60%.

[0093] As can be seen from Examples 1-1, 1-17 to 1-22, 1-39, and 1-40, when the second group of lithium nickel cobalt manganese oxide ternary materials is located in the first cathode material layer and the first group of lithium nickel cobalt manganese oxide ternary materials is located in the second cathode material layer, by adjusting the mass percentages a2 and b2 of the two groups of lithium nickel cobalt manganese oxide ternary materials in the first and second cathode material layers to satisfy 25%≤a2≤95% and 5%≤b2≤75%, the discharge time of the secondary battery at 0°C low temperature conditions at 1C and 0.5C rates is improved, thus indicating that the discharge performance of lithium-ion batteries at low temperature and low SOC conditions is improved. From Examples 1-17 to 1-22, it can be seen that the discharge time of the two groups of lithium nickel cobalt manganese oxide ternary materials first increases and then decreases as the mass percentages a2 and b2 increase, indicating that the mass percentages a2 and b2 of the lithium nickel cobalt manganese oxide ternary materials have preferred ranges: 35% ≤ a2 ≤ 80% and 20% ≤ b2 ≤ 65%. Further, 45% ≤ a2 ≤ 65% and 35% ≤ b2 ≤ 55%.

[0094] The particle size of the two sets of lithium nickel cobalt manganese oxide ternary materials affects the low-temperature discharge performance of the secondary battery. As can be seen from Examples 1-1, 1-23 to 1-34 and Comparative Example 1, the low-temperature discharge performance of the secondary battery can be affected by adjusting the particle size D of the two sets of lithium nickel cobalt manganese oxide ternary materials. V1 50 and D V250. Within the scope of this application, the discharge time of the secondary battery at 0°C and discharge rates of 1C and 0.5C is improved, indicating that the discharge performance of the lithium-ion battery at low temperature and low SOC is improved. From the discharge times of Examples 1-1, 1-23 to 1-34 at 0°C and discharge rates of 1C and 0.5C, it can be concluded that the particle size D of the lithium nickel cobalt manganese oxide ternary material... V1 50 has a significant impact on discharge time, D V2 The influence of 50 is relatively small, which indicates that the particle size of the cobalt-manganese ternary material has an optimal range.

[0095] The content of conductive agent affects the low-temperature discharge performance of secondary batteries. As can be seen from Examples 1-1, 1-35, 1-36 and Comparative Example 1, by adjusting the content of conductive agent within the scope of this application, the discharge time of secondary batteries at 0°C low temperature conditions at 1C and 0.5C rates is improved, thus indicating that the discharge performance of lithium-ion batteries at low temperature and low SOC conditions is improved.

[0096] Table 2 shows the secondary batteries made by mixing two or more lithium nickel cobalt manganese oxide ternary materials. As can be seen from Examples 1-1, 1-41 to 1-43 and Comparative Example 1, by adjusting the types and contents of two or more lithium nickel cobalt manganese oxide ternary materials within the scope of this application, the discharge time of the secondary battery at 0°C low temperature conditions at 1C and 0.5C rates is improved. Comparing Examples 1-41 with Example 1-1, Example 1-41 added a set of ternary materials with high cobalt content (0.15≤y≤0.60). The increased cobalt content lowered the discharge voltage plateau and improved the material impedance, resulting in improved discharge performance. Comparing Examples 1-42 with Example 1-1, Example 1-42 added a set of ternary materials with low cobalt content (0<y≤0.14), which lowered the discharge voltage, but had a smaller improvement on the material impedance, thus having a certain impact on discharge performance. Comparing Examples 1-43 with Example 1-1, Example 1-43 added both a set of ternary materials with high cobalt content and a set with low cobalt content. The increased cobalt content lowered the discharge voltage plateau and improved the material impedance, thereby improving discharge performance.

[0097] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrochemical device comprising a positive electrode, the positive electrode comprising a current collector and a positive electrode material layer located on at least one surface of the current collector in the thickness direction, the positive electrode material layer comprising a first positive electrode material layer and a second positive electrode material layer, the second positive electrode material layer being located between the first positive electrode material layer and the current collector, the positive electrode layer comprising a positive electrode active material, the positive electrode active material comprising two or more ternary materials of lithium nickel cobalt manganese oxide, wherein... The two or more lithium nickel cobalt manganese oxide ternary materials are divided into two groups. The chemical formula of the first group of lithium nickel cobalt manganese oxide ternary materials is Li. n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, the two sets of lithium nickel cobalt manganese oxide ternary materials are located in the first cathode material layer and the second cathode material layer, respectively.

2. The electrochemical device according to claim 1, wherein, The materials of M1 and M2 are each independently selected from at least one of Ag, Sn, Zn, Al, Mo, Cu, B, Ti and Fe.

3. The electrochemical device according to claim 1, wherein, 0.15≤y1≤0.45, 0.02<y2≤0.

08.

4. The electrochemical device according to claim 1, wherein, The first group of lithium nickel cobalt manganese oxide ternary materials is located in the first cathode material layer, and the second group of lithium nickel cobalt manganese oxide ternary materials is located in the second cathode material layer. Based on the total mass of the lithium nickel cobalt manganese oxide ternary materials, the mass percentage of the first group of lithium nickel cobalt manganese oxide ternary materials is a1, and the mass percentage of the second group of lithium nickel cobalt manganese oxide ternary materials is b1, where 5% ≤ a1 ≤ 70% and 30% ≤ b1 ≤ 95%.

5. The electrochemical device according to claim 4, wherein, 25% ≤ a1 ≤ 65%, 35% ≤ b1 ≤ 75%.

6. The electrochemical device according to claim 5, wherein, 40% ≤ a1 ≤ 60%, 40% ≤ b1 ≤ 60%.

7. The electrochemical device according to claim 1, wherein, The second group of lithium nickel cobalt manganese oxide ternary materials is located in the first cathode material layer, and the first group of lithium nickel cobalt manganese oxide ternary materials is located in the second cathode material layer. Based on the total mass of the lithium nickel cobalt manganese oxide ternary materials, the mass percentage of the first group of lithium nickel cobalt manganese oxide ternary materials is a2, and the mass percentage of the second group of lithium nickel cobalt manganese oxide ternary materials is b2, where 25% ≤ a2 ≤ 95% and 5% ≤ b2 ≤ 75%.

8. The electrochemical device according to claim 7, wherein, 35% ≤ a2 ≤ 80%, 20% ≤ b2 ≤ 65%.

9. The electrochemical device according to claim 8, wherein, 45% ≤ a² ≤ 65%, 35% ≤ b² ≤ 55%.

10. The electrochemical device according to claim 1, wherein, The coating weight of the positive electrode material layer is 6 mg / cm³. 2 Up to 11 mg / cm 2 .

11. The electrochemical device according to claim 1, wherein, The particle size of the first group of lithium nickel cobalt manganese oxide ternary materials is D. V1 50, 1μm≤D V1 50≤10μm.

12. The electrochemical device according to claim 11, wherein, 2μm≤D V1 50≤9μm。 13. The electrochemical device according to claim 1, wherein, The particle size of the second group of lithium nickel cobalt manganese oxide ternary materials is D. V2 50, 1μm≤D V2 50≤15μm.

14. The electrochemical device according to claim 13, wherein, 2μm≤D V2 50≤10μm。 15. The electrochemical device according to claim 1, wherein, 0.95≤n1≤1.05, 0.3≤x1≤0.84, 0.01≤z1≤0.7, 0≤m1≤0.2; 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, 0≤m2≤0.

2.

16. The electrochemical device according to claim 1, wherein, The positive electrode active material includes two ternary materials, NCM-1 and NCM-2, of lithium nickel cobalt manganese oxide. NCM-1 satisfies: 0.15≤y≤0.60, and NCM-2 satisfies: 0<y≤0.

14.

17. The electrochemical device according to claim 1, wherein, Based on the mass of the cathode material layer, the mass percentage of the lithium nickel cobalt manganese oxide ternary material is 90% to 98%.

18. The electrochemical device according to claim 1, wherein, The positive electrode material layer further includes a conductive agent and a binder. The conductive agent is made of at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The binder is made of at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, and potassium hydroxymethyl cellulose. Based on the mass of the positive electrode material layer, the conductive agent has a mass percentage content of 1% to 8%, and the binder has a mass percentage content of 1% to 3%.

19. A method for preparing the electrochemical device according to any one of claims 1 to 18, comprising: Preparation of the positive electrode: The two groups of lithium nickel cobalt manganese oxide ternary materials are divided into two groups of positive electrode active materials. The first group of lithium nickel cobalt manganese oxide ternary materials has the chemical formula Li. n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, satisfying 0.15≤y1≤0.60, the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, the two sets of positive electrode active materials are respectively disposed in the first positive electrode material layer and the second positive electrode material layer to obtain the positive electrode sheet.

20. An electronic device comprising the electrochemical device according to any one of claims 1 to 18.

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