Electrochemical device and electronic device comprising same

Abstract

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, and the positive pole active material comprises two or more nickel cobalt lithium manganate ternary materials; the two or more nickel cobalt lithium manganate ternary materials are divided into two groups, the chemical formula of the first group of nickel cobalt lithium manganate ternary materials is Lin1Nix1Coy1Mnz1M1m1O2, x1 + y1 + z1 + m1 = 1 and meets 0.15 < = y1 < = 0.60, and the chemical formula of the second group of nickel cobalt lithium manganate ternary materials is Lin2Nix2Coy2Mnz2M2m2O2, x2 + y2 + z2 + m2 = 1 and meets 0 < y2 < = 0.14; based on the total mass of the nickel cobalt lithium manganate ternary materials, the mass percentage content of the first group of nickel cobalt lithium manganate ternary materials is a, the mass percentage content of the second group of nickel cobalt lithium manganate ternary materials is b, a is more than or equal to 10% and less than or equal to 80%, and b is more than or equal to 20% and less than or equal to 90%. By regulating and controlling the type and content of the positive electrode active material in the application range, the discharge performance of the NCM lithium battery in a low-temperature and low-SOC state can be improved.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to an electrochemical device and a preparation method thereof. Background Art

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

[0003] However, current NCM lithium batteries quickly reach the discharge cut-off voltage (3.0V) when discharged at low temperatures and low state of charge (SOC), significantly deteriorating their performance and making it difficult to meet the demands of actual product applications. Lithium batteries using lithium cobalt oxide as the positive electrode material can meet these demands, but lithium cobalt oxide consumes relatively scarce cobalt metal resources, resulting in high costs and hindering the cost reduction of battery cells. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode plate and an electrochemical device to improve the discharge performance of NCM lithium batteries under low temperature and low SOC conditions.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrochemical device, comprising a positive electrode plate, the positive electrode plate comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, wherein the positive electrode active material comprises two or more nickel cobalt lithium manganese oxide ternary materials; the two or more nickel cobalt lithium manganese oxide ternary materials are divided into two groups, the chemical formula of the first group of nickel cobalt lithium 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 nickel cobalt manganese oxide lithium ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14. By using two or more nickel-cobalt-manganese oxide ternary materials with different cobalt contents, the discharge performance of NCM lithium batteries at low temperature and low SOC can be improved.

[0007] In one embodiment of the present application, based on the total mass of the nickel-cobalt-manganese oxide ternary material, the mass percentage of the first group of nickel-cobalt-manganese oxide ternary materials is a, and the mass percentage of the second group of nickel-cobalt-manganese oxide ternary materials is b, 10%≤a≤80%, 20%≤b≤90%; preferably, 30%≤a≤60%, 40%≤b≤70%; further preferably, 40%≤a≤60%, 40%≤b≤60%. By regulating the content of nickel-cobalt-manganese oxide ternary materials with different cobalt contents within the scope of this application, the discharge performance of the NCM lithium battery at low temperature and low SOC can be improved.

[0008] In one embodiment of the present application, the nickel cobalt lithium manganese oxide ternary material may include doping or coating elements, and the materials of M1 and M2 are 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 denser and have better kinetic performance; on the other hand, it can reduce the specific surface area of the positive electrode active material and reduce the side reaction between the positive electrode active material and the electrolyte; on the other hand, it is conducive to the formation of a passivation film on the surface of the positive electrode active material particles, thereby improving its first effect 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, that is, the nickel-cobalt-manganese ternary material may not include doping or coating elements.

[0009] In one embodiment of the present application, two or more nickel-cobalt-manganese oxide ternary materials are divided into two groups according to the value of y. The first group of nickel-cobalt-manganese oxide ternary materials satisfies 0.15≤y1≤0.50, and the second group of nickel-cobalt-manganese oxide ternary materials satisfies 0.02≤y2≤0.10. By regulating the molar amount of cobalt atoms in the nickel-cobalt-manganese oxide ternary materials within the range of the present application, the impedance of the battery can be reduced, and the battery discharge voltage platform can be stabilized, which is conducive to extending the low-temperature discharge time of the battery.

[0010] In one embodiment of the present application, the particle size of the first group of nickel cobalt lithium manganese oxide ternary materials is D V1 50, 1μm≤D V1 50≤10μm, preferably, 2μm≤D V1By adjusting the particle size of the lithium nickel cobalt manganese oxide material within the scope of this application, the distance of lithium ion transmission during battery charging and discharging can be improved, thereby extending the discharge time of the battery in a low temperature environment.

[0011] In one embodiment of the present application, the particle size of the second group of nickel cobalt lithium manganese oxide ternary materials is D V2 50, 1μm≤D V2 50≤15μm, optionally, 2μm≤D V2 By adjusting the particle size of the lithium nickel cobalt manganese oxide material within the scope of this application, the distance of lithium ion transmission during battery charging and discharging can be improved, thereby extending the discharge time of the battery in a low temperature environment.

[0012] In one embodiment of the present application, 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, 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 nickel cobalt manganese oxide lithium ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, among which, 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, 0≤m2≤0.2.

[0013] In one embodiment of the present application, the positive electrode active material includes two nickel-cobalt-manganese oxide ternary materials, NCM-1 and NCM-2, wherein NCM-1 satisfies the following conditions: 0.15≤y1≤0.60, and NCM-2 satisfies the following conditions: 0<y2≤0.14. By regulating the range of the cobalt content y of the nickel-cobalt-manganese oxide ternary material within the scope of the present application, preferably using two nickel-cobalt-manganese oxide ternary materials, it is possible to reduce the battery impedance while increasing the battery discharge voltage platform, thereby improving the battery's discharge capacity in low temperature environments.

[0014] In one embodiment of the present application, the positive electrode material layer also includes a conductive agent and a binder, the material of the conductive agent is selected from at least one of conductive carbon black and carbon nanotubes, and the material of the binder is selected from at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose and potassium hydroxymethyl cellulose.

[0015] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage of the conductive agent is 1% to 8%, and the mass percentage of the binder is 1% to 3%.

[0016] A second aspect of the present application provides a method for preparing the electrochemical device according to any of the aforementioned embodiments.

[0017] Two or more nickel-cobalt-manganese oxide ternary materials are mixed to obtain a positive electrode active material; wherein the two or more nickel-cobalt-manganese oxide ternary materials used are divided into two groups, the chemical formula of the first group of 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 nickel cobalt manganese oxide lithium ternary material is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14; disposing the positive electrode active material on at least one surface of the positive electrode current collector in the thickness direction to obtain a positive electrode sheet. By regulating the preparation method of the electrochemical device, the electrical device provided in this application can have good performance.

[0018] A third aspect of the present application provides an electronic device comprising the electrochemical device according to any one of the aforementioned embodiments.

[0019] Beneficial effects of this application:

[0020] The present application provides an electrochemical device, the electrochemical device includes a positive electrode plate, the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes a positive electrode active material, the positive electrode active material includes two or more nickel cobalt lithium manganese oxide ternary materials, the two or more nickel cobalt lithium manganese oxide ternary materials are divided into two groups, the chemical formula of the first group of nickel cobalt lithium 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 nickel cobalt manganese oxide lithium ternary material is Li n2 Ni x2 Co y2 Mn z2 M2 m2O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14. By adjusting the type and content of the positive electrode active material within the scope of this application, the discharge performance of the NCM lithium battery at low temperature and low SOC state can be improved.

[0021] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0022] To make the purpose, technical solutions, and advantages of this application more clearly understood, the following examples are given to further describe this application in detail. Obviously, the described examples are only some examples of this application, rather than all examples. All other examples obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0023] It should be noted that in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0024] The present application provides an electrochemical device, which includes a positive electrode plate, which includes a positive electrode material layer, which includes a positive electrode active material, which includes two or more nickel cobalt manganese oxide ternary materials, wherein the nickel cobalt manganese oxide ternary material is a layered structure. The chemical formula of the nickel cobalt manganese oxide ternary material is Li n Ni x Co y Mn z M m O2, x+y+z+m=1; the molar mass of cobalt atoms in the nickel-cobalt-manganese oxide ternary material is y, and two or more nickel-cobalt-manganese oxide ternary materials are divided into two groups according to the value of y. The chemical formula of the first group of 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 nickel cobalt manganese oxide lithium ternary material is Li n2 Ni x2 Co y2 Mn z2 M2 m2O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14, preferably, 0.15≤y1≤0.50, 0.02≤y2≤0.10, illustratively, y1 can be 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60 or a range consisting of any two of the above values, y2 can be 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14 or a range consisting of any two of the above values.

[0025] The inventors have found that when the nickel-cobalt-manganese oxide ternary material is used as the positive electrode active material, it quickly reaches the discharge cut-off voltage (3.0V) during low-temperature and low-SOC discharge, and the low-temperature and low-SOC discharge performance deteriorates significantly, making it difficult to meet the actual product application requirements. Usually, lithium cobalt oxide materials are used to replace the nickel-cobalt-manganese oxide ternary material to achieve discharge performance that meets the requirements under low-temperature and low-SOC environments. However, the lithium cobalt oxide material requires the consumption of cobalt metal resources with relatively lower reserves, and the cost is high, which is not conducive to reducing the cost of the battery cell. When the cobalt content in the nickel-cobalt-manganese oxide ternary material is high (for example, 0.15≤y≤0.60), the discharge voltage of the ternary material is lower and the discharge curve is flatter; when the cobalt content in the nickel-cobalt-manganese oxide ternary material is low (for example, 0<y≤0.14), the discharge voltage of the ternary material is higher and the slope of the discharge curve is larger. After mixing two or more nickel-cobalt-manganese oxide ternary materials that meet the above range, it can simultaneously have the characteristics of high discharge voltage and flat discharge curve, thereby improving the low-temperature discharge capability. Increasing the cobalt content in the ternary material can reduce the impedance of the battery and at the same time reduce the discharge voltage platform. The reduced impedance is conducive to extending the low-temperature discharge time of the battery, but the reduced discharge voltage will shorten the low-temperature discharge time of the battery. Therefore, the cobalt content can have a relatively preferred range based on experimental results.

[0026] Based on the total mass of the nickel-cobalt-lithium-manganese-oxide ternary material, the mass percentage of the first group of nickel-cobalt-lithium-manganese-oxide ternary materials is a, and the mass percentage of the second group of nickel-cobalt-lithium-manganese-oxide ternary materials is b, 10%≤a≤80%, 20%≤b≤90%, preferably, 30%≤a≤60%, 40%≤b≤70%, further preferably, 40%≤a≤60%, 40%≤b≤60%. Illustratively, a can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range consisting of any two of the above values, and b can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or a range consisting of any two of the above values. After two or more nickel-cobalt-manganese oxide ternary materials are mixed, by regulating the mass percentages a and b (for example, a=80%, b=20%) of the two nickel-cobalt-manganese oxide ternary materials with higher and lower cobalt element contents based on the total mass of the positive electrode active material, the mixed nickel-cobalt-manganese oxide ternary material can have a high discharge voltage and a relatively flat discharge curve. Thus, by regulating the type and content of the nickel-cobalt-manganese oxide ternary material within the above range, the discharge performance of the NCM lithium battery under low temperature and low SOC conditions can be improved.

[0027] In one embodiment of the present application, the nickel cobalt lithium manganese oxide ternary material may include doping or coating elements, and the materials of M1 and M2 are 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 denser and have better kinetic performance; on the other hand, it can reduce the specific surface area of the positive electrode active material and reduce the side reaction between the positive electrode active material and the electrolyte; on the other hand, it is conducive to the formation of a passivation film on the surface of the positive electrode active material particles, thereby improving its first effect 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, that is, the nickel-cobalt-manganese ternary material may not include doping or coating elements.

[0028] In one embodiment of the present application, the particle size of the first group of nickel cobalt lithium manganese oxide ternary materials is D V1 50, 1μm≤D V150≤10μm, preferably, 2μm≤D V1 50≤9μm, illustratively, D V1 50 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm or a range consisting of any two of the above values. The particle size of the second group of nickel cobalt manganese oxide lithium ternary materials is D V2 50, 1μm≤D V2 50≤15μm, preferably, 2μm≤D V2 50≤10μm, illustratively, D V2 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 consisting of any two of the above values. The particle size of the nickel cobalt manganese oxide ternary material will affect the distance of lithium ion transmission during battery charging and discharging. The greater the transmission distance, the worse the discharge time at low temperature. By regulating the particle size of the nickel cobalt manganese oxide material within the scope of this application, the distance of lithium ion transmission during battery charging and discharging can be improved, thereby extending the discharge time of the battery in a low temperature environment.

[0029] In one embodiment of the present application, 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, 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 nickel cobalt manganese oxide lithium ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, among which, 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, 0≤m2≤0.2.

[0030] In one embodiment of the present application, the positive electrode active material includes two nickel cobalt manganese oxide ternary materials, which are grouped according to the cobalt element content y and are divided 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 a range consisting of any 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 a range consisting of any two of the above values. By regulating the range of the cobalt content y of the nickel cobalt manganese oxide ternary material within the scope of this application, it is preferred to use two nickel cobalt manganese oxide ternary materials, which can reduce the battery impedance while improving the battery discharge voltage platform, thereby improving the discharge capacity of the battery in a low temperature environment and simplifying the production process.

[0031] In this application, the preparation method of the nickel-cobalt-lithium manganese oxide ternary material is not particularly limited, as long as it can achieve the purpose of the present invention. For example, it can be prepared by the following method:

[0032] Nitrates, sulfates or chlorides of Ni, Co and Mn are co-precipitated under the action of ammonia water or ammonium bicarbonate chelating agent to prepare NCM carbonate or hydroxide precursors, and then the precursors are sintered with lithium hydroxide or lithium carbonate at a high temperature of 700℃ to 1000℃ to obtain nickel cobalt manganese oxide ternary material.

[0033] In the present application, the positive electrode material layer further includes a conductive agent and a binder. The material of the conductive agent is selected from at least one of conductive carbon black and carbon nanotubes. For example, 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 material of the binder is selected from at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, and potassium hydroxymethyl cellulose.

[0034] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage of the conductive agent is 1% to 8%. For example, the mass percentage 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 a range consisting of any two of the above values; the mass percentage of the binder is 1% to 3%. For example, the mass percentage 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 a range consisting of any two of the above values. By regulating the type and content of the conductive agent and the binder within the above range, the discharge performance of the NCM lithium battery at low temperature and low SOC can be improved.

[0035] The positive electrode sheet of the present application also includes a positive electrode current collector. The present application has no special restrictions on the positive electrode current collector, as long as it can achieve the purpose of the present application. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0036] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0037] In the present application, the electrochemical device further comprises 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 "surface" here can be the entire surface area of the negative electrode current collector or a partial surface area of the negative electrode current collector. This is not particularly limited in the present application, as long as the purpose of the present application can be achieved.

[0038] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0039] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0040] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and binder, as long as they can achieve the purpose of the present application. For example, they can be at least one of the above-mentioned conductive agents and binders. The present application does not particularly limit 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 they can achieve the purpose of the present application.

[0041] The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0042] The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0043] Optionally, the negative electrode sheet may further include a conductive layer positioned 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 any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the above-mentioned conductive agents and binders.

[0044] In the present application, the electrochemical device also includes a diaphragm. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0045] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0046] 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 a polymer and an inorganic layer.

[0047] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The application is not particularly limited to inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The application is not particularly limited to the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0048] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0049] The second aspect of the present application provides a method for preparing an electrochemical device according to any of the aforementioned embodiments. Two or more nickel-cobalt-manganese oxide ternary materials are mixed to obtain a positive electrode active material; wherein the two or more nickel-cobalt-manganese oxide ternary materials used are divided into two groups, and the chemical formula of the first group of 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 nickel cobalt manganese oxide lithium ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.14; disposing the positive electrode active material on at least one surface of the positive electrode current collector in the thickness direction to obtain a positive electrode sheet.

[0050] The third aspect of the present application provides an electronic device, which includes the electrochemical device in any of the aforementioned embodiments. The electronic device provided in the present application has good performance. The present application does not particularly limit the type of electronic device, and it 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 head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor, etc.

[0051] Example

[0052] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0053] Test methods and equipment:

[0054] Cobalt content test:

[0055] Using a scanning electron microscope (SEM), NCM material particles were selected, and an energy dispersive spectrometer (EDS) was used to analyze the element types of the selected NCM particles. It should be noted that the mass of each element is obtained by using the EDS test. If you want to obtain the molar amount of each element's atoms, you need to convert it according to the following formula: n'=m' / M', where n' is the molar amount of each element's atoms, m' is the mass of each element measured using EDS, and M' is the molar mass of each element. Therefore, the molar amount of cobalt atoms in the nickel cobalt manganese oxide lithium ternary material is n'(Co)=m'(Co) / M'(Co).

[0056] Test of the content of each component in the positive electrode active material layer:

[0057] The prepared positive electrode plate was calcined at 500°C for 4 hours in an oxygen-filled environment to remove the carbon-containing conductive agent and organic binder components in the plate. The powder after high-temperature treatment was evenly dispersed in water, and 1 mL of the suspension was dried and sampled. SEM and EDS were used for observation at a magnification of 1000 times. 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.

[0058] Particle size test:

[0059] The suspension is dried and sampled. When observed using SEM and EDS, in addition to counting the composition and particle number, the particle size is also counted to obtain the Dv50 of different components.

[0060] Low temperature discharge performance test

[0061] The battery was subjected to a low-temperature and low-SOC discharge test: the battery was discharged at a 0.2C discharge rate to 3.0V, then charged at a rate of 0.2C for 0.5H. The battery was placed at a low temperature of 0°C and discharged at rates of 1C and 0.5C respectively, and the duration of discharge to 3.0V was recorded.

[0062] Example 1-1

[0063] <Preparation of positive electrode sheet>

[0064] The mass ratio of LiNi is 1:1 0.5 Co 0.4 Mn 0.09 Al 0.01 O2 and 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 75wt%, which was then stirred to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm. The coating weight of the positive electrode active material layer on the positive electrode sheet was 180g / m 2 , and dried at 90°C to obtain a positive electrode sheet coated on one side with a positive electrode active material layer. Then repeat the above steps on the other side of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer. After coating, the positive electrode sheet is cold pressed to a compaction density of 4.1g / cm 3 After cutting and welding the tabs, the positive electrode sheet with a specification of 74mm×867mm is obtained for use.

[0065] <Preparation of negative electrode sheet>

[0066] The negative electrode active materials, artificial graphite, conductive carbon black (Super P), and polyacrylic acid, were mixed in a weight ratio of 97.3:1.5:1.2, and deionized water (H2O) was added as a solvent to prepare a slurry with a solid content of 70 wt%. The mixture was stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on one surface of a 10 μm thick negative electrode current collector copper foil. The coating weight of the negative electrode active material layer on the negative electrode sheet was 95 g / m 2 , and dried at 110°C to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. Then repeat the above steps on the other side of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. After coating, the negative electrode sheet is cold pressed to a compaction density of 1.7g / cm 3 After cutting and welding the tabs, the negative electrode sheet with a specification of 78mm×875mm is obtained for use. Among them, the negative electrode active material artificial graphite is adjusted by adjusting the ball milling time to make its Dv50 10μm and the specific surface area 1.6m 2 / g.

[0067] <Preparation of Electrolyte>

[0068] In an argon atmosphere 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 in a mass ratio of EC:EMC:DEC = 3:5:2 to obtain a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and mixed uniformly to obtain an electrolyte. The lithium salt content was 12.5% by weight of the electrolyte, with the remainder being the base solvent.

[0069] <Diaphragm>

[0070] A polyethylene film with a thickness of 9 μm was selected as the separator.

[0071] <Preparation of lithium-ion batteries>

[0072] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an outer packaging foil, and then the prepared electrolyte is injected, and after processes such as formation, degassing, and trimming, a lithium-ion battery is obtained.

[0073] Example 1-2 to Example 1-32

[0074] Except for changing the preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0075] Examples 1-33

[0076] The mass ratio of LiNi is 25%:50%:25%.0.5 Co 0.4 Mn 0.09 Al 0.01 O2、LiNi 0.5 Co 0.05 Mn 0.44 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), 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 75wt%, which was then stirred to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm. The coating weight of the positive electrode active material layer on the positive electrode sheet was 180g / m 2 The positive electrode sheet with a positive electrode active material layer coated on one side was obtained by drying at 90°C. The rest was the same as in Example 1-1, and a low-temperature discharge performance test was performed.

[0077] Examples 1-34

[0078] LiNi with a mass ratio of 50%:25%:25% 0.5 Co 0.4 Mn 0.09 Al 0.01 O2、LiNi 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, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%, which was then stirred to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm. The coating weight of the positive electrode active material layer on the positive electrode sheet was 180g / m 2 The positive electrode sheet with a positive electrode active material layer coated on one side was obtained by drying at 90°C. The rest was the same as in Example 1-1, and a low-temperature discharge performance test was performed.

[0079] Examples 1-35

[0080] The mass ratio of LiNi is 25%:25%:25%:25%0.5 Co 0.4 Mn 0.09 Al 0.01 O2、LiNi 0.5 Co 0.05 Mn 0.44 Al 0.01 O2、LiNi 0.4 Co 0.5 Mn 0.09 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, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%, which was then stirred to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm. The coating weight of the positive electrode active material layer on the positive electrode sheet was 180g / m 2 , and dried at 90°C to obtain a positive electrode sheet coated with a positive electrode active material layer on one side. The rest was the same as in Example 1-1, and a low-temperature discharge performance test was performed.

[0081] Comparative Example 1

[0082] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.

[0083]

[0084]

[0085]

[0086] Table 2

[0087] Group 0℃0.5C discharge time 0℃1C discharge time Examples 1-33 6min16s 2min20s Examples 1-34 6min11s 2min16s Examples 1-35 6 minutes and 15 seconds 2min16s

[0088] As can be seen from Examples 1-1 to 1-11 and Comparative Example 1, by regulating the cobalt contents y1 and y2 in the two groups of nickel-cobalt-manganese-lithium ternary materials within the range of this application, the discharge time of the secondary battery at 0°C low temperature conditions at 1C and 0.5C rates is improved, thereby demonstrating that the discharge performance of the lithium-ion battery at low temperature and low SOC is improved. Based on the discharge times at 0°C low temperature conditions at 1C and 0.5C rates in Examples 1-1 to 1-11, it can be concluded that the cobalt contents y1 and y2 are within a preferred range.

[0089] Based on the total mass of the positive electrode active material, the mass percentage of the two groups of nickel cobalt manganese oxide ternary materials will affect the low-temperature discharge performance of the secondary battery. It can be seen from Examples 1-1, 1-12 to 1-16 and 1-31 and 1-32 that by regulating the mass percentages a and b of the two groups of nickel cobalt manganese oxide ternary materials to meet the following conditions: 10% ≤ a ≤ 80%, 20% ≤ b ≤ 90%, the discharge time of the secondary battery at 1C and 0.5C rates under low temperature conditions of 0°C is improved, indicating that the discharge performance of the lithium-ion battery at low temperature and low SOC conditions is improved. From the discharge times of Examples 1-1, 1-12 to 1-16, 1-31, and 1-32 at 0°C low temperature conditions at 1C and 0.5C rates, it can be concluded that the mass percentages a and b of the nickel-cobalt-manganese-oxide lithium ternary material first increase and then decrease with increasing a, indicating that the mass percentages a and b of the nickel-cobalt-manganese-oxide lithium ternary material have a preferred range of 30% ≤ a ≤ 60% and 40% ≤ b ≤ 70%. Furthermore, a and b have a more preferred range of 40% ≤ a ≤ 60% and 40% ≤ b ≤ 60%.

[0090] The particle size of the two groups of nickel cobalt manganese oxide ternary materials will affect the low temperature discharge performance of the secondary battery. It can be seen from Examples 1-1, 1-17 to 1-28 and Comparative Example 1 that by adjusting the particle size D of the two groups of nickel cobalt manganese oxide ternary materials, the low temperature discharge performance of the secondary battery can be improved. V1 50 and D V2 50 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, which shows that the discharge performance of the lithium-ion battery at low temperature and low SOC state is improved. From the discharge time of Examples 1-1, 1-17 to 1-28 at 0°C low temperature conditions at 1C and 0.5C rates, it can be concluded that the particle size D of the nickel cobalt manganese oxide ternary material is V1 50 has a greater impact on the discharge time, D V2 The influence of 50 is small, which shows that the particle size of the cobalt-manganese ternary material has an optimal range.

[0091] The content of the conductive agent will affect the low-temperature discharge performance of the secondary battery. It can be seen from Example 1-1, Example 1-29, Example 1-30 and Comparative Example 1 that by adjusting the content of the conductive agent within the scope of this application, the discharge time of the secondary battery at a low temperature of 0°C and a discharge rate of 1C and 0.5C is improved, indicating that the discharge performance of the lithium-ion battery at a low temperature and low SOC state is improved.

[0092] The secondary batteries made by mixing two or more nickel cobalt manganese oxide ternary materials are shown in Table 2. It can be seen from Example 1-1 and Example 1-33 to Example 1-35 and Comparative Example 1 that by regulating the types and contents of two or more nickel cobalt manganese oxide ternary materials within the scope of this application, the discharge time of the secondary battery at 1C and 0.5C rates under low temperature conditions of 0°C is improved. Comparing Example 1-33 with Example 1-1, Example 1-33 adds a group of ternary materials with high cobalt content (0.15≤y≤0.60), and the cobalt content is increased, which reduces the discharge voltage platform and improves the material impedance, thereby improving the discharge performance; Comparing Example 1-34 with Example 1-1, Example 1-34 adds a group of ternary materials with low cobalt content (0<y≤0.14), which reduces the discharge voltage, but has little improvement on the material impedance, thereby having a certain impact on the discharge performance; Comparing Example 1-35 with Example 1-1, Example 1-35 simultaneously adds a group of ternary materials with high cobalt content and a group of ternary materials with low cobalt content, and the cobalt content is increased, which reduces the discharge voltage platform while improving the material impedance, thereby improving the discharge performance.

[0093] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material, wherein: The positive electrode active material includes two or more nickel cobalt manganese oxide ternary materials; the two or more nickel cobalt manganese oxide ternary materials are divided into two groups, the chemical formula of the first group of 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 nickel cobalt manganese oxide lithium ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0<y2≤0.

14.

2. The electrochemical device according to claim 1, wherein Based on the total mass of the nickel-cobalt-lithium-manganese-oxide ternary material, the mass percentage of the first group of nickel-cobalt-lithium-manganese-oxide ternary materials is a, and the mass percentage of the second group of nickel-cobalt-lithium-manganese-oxide ternary materials is b, 10%≤a≤80%, 20%≤b≤90%.

3. 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.

4. The electrochemical device according to claim 2 or 3, wherein 30%≤a≤60%, 40%≤b≤70%.

5. The electrochemical device according to claim 4, wherein 40%≤a≤60%, 40%≤b≤60%.

6. The electrochemical device according to any one of claims 1 to 5, wherein 0.15≤y1≤0.50, 0.02≤y2≤0.

10.

7. The electrochemical device according to any one of claims 1 to 6, wherein The particle size of the first group of nickel cobalt lithium manganese oxide ternary materials is D V1 50, 1μm≤D V1 50≤10μm.

8. The electrochemical device according to claim 7, wherein 2μm≤D V1 50≤9μm。 9. The electrochemical device according to any one of claims 1 to 8, wherein The particle size of the second group of nickel cobalt lithium manganese oxide ternary materials is D V2 50, 1μm≤D V2 50≤15μm.

10. The electrochemical device according to claim 9, wherein 2μm≤D V2 50≤10μm。 11. 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.

12. The electrochemical device according to claim 1, wherein The positive electrode active material includes two nickel cobalt lithium manganese oxide ternary materials NCM-1 and NCM-2, NCM-1 satisfies: 0.15≤y1≤0.60, and NCM-2 satisfies: 0<y2≤0.

14.

13. The electrochemical device according to any one of claims 1 to 12, wherein The positive electrode material layer also includes a conductive agent and a binder, the material of the conductive agent is selected from at least one of conductive carbon black and carbon nanotubes, and the material of the binder is selected from at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose and potassium hydroxymethyl cellulose.

14. The electrochemical device according to claim 13, wherein Based on the mass of the positive electrode material layer, the mass percentage of the conductive agent is 1% to 8%, and the mass percentage of the binder is 1% to 3%.

15. A method for preparing the electrochemical device according to any one of claims 1 to 14, comprising: Prepare the positive electrode sheet: mix the two or more nickel cobalt manganese oxide ternary materials to obtain the positive electrode active material; wherein the two or more nickel cobalt manganese oxide ternary materials used are divided into two groups, the chemical formula of the first group of 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 nickel cobalt manganese oxide lithium 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 positive electrode active material is arranged on at least one surface in the thickness direction of the positive electrode collector to obtain a positive electrode sheet.

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

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