Electrochemical device and electronic device comprising same

Abstract

An electrochemical device. The electrochemical device comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode material layer. The positive electrode material layer comprises a positive electrode active material. The positive electrode active material includes two or more lithium nickel cobalt manganese oxide (NCM) ternary materials. The two or more NCM ternary materials are divided into two groups; the chemical formula of the first group of NCM ternary materials is Lin1Nix1Coy1Mnz1M1m1O2, wherein x1+y1+z1+m1=1, and 0.15≤y1≤0.60; and the chemical formula of the second group of NCM ternary materials is Lin2Nix2Coy2Mnz2M2m2O2, wherein x2+y2+z2+m2=1, and 0<y2≤0.14. On the basis of the total mass of the NCM ternary materials, the mass percentage content of the first group of NCM ternary materials is a, and the mass percentage content of the second group of NCM ternary materials is b, wherein 10%≤a≤80%, and 20%≤b≤90%. By regulating the type and content of the positive electrode active material within the ranges in the present application, the discharge performance of NCM lithium batteries under low-temperature and low-SOC conditions can be improved.

Description

An electrochemical device and an electronic device including the same TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, and in particular to an electrochemical device and a preparation method thereof. BACKGROUND

[0002] The positive active material of a lithium ion battery includes lithium nickel cobalt manganese oxide ternary material (NCM), lithium cobaltate, etc. The lithium battery with lithium nickel cobalt manganese oxide ternary material as the positive active material has the advantages of low cost, high specific capacity, and good safety.

[0003] However, the NCM lithium battery currently reaches the discharge cut-off voltage (3.0V) quickly when discharging at low temperature and low state of charge (SOC), and the low-temperature low-SOC discharge performance deteriorates significantly, which is difficult to meet the actual product application requirements. The lithium battery using lithium cobaltate as the positive material can meet the demand for low-temperature low-SOC discharge, but the lithium cobaltate material needs to consume a relatively lower cobalt metal resource, which is high in cost and is not conducive to reducing the cost of the battery cell.

[0004] SUMMARY

[0005] The purpose of the present application is to provide a positive electrode sheet and an electrochemical device to improve the discharge performance of the NCM lithium battery at low temperature and low SOC.

[0006] It should be noted that the present application is explained by taking a lithium ion battery as an example of a secondary battery in the summary of the application, but the secondary battery of the present application is not limited to a lithium ion battery. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides an electrochemical device, comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising a positive active material, wherein the positive active material comprises two or more kinds of lithium nickel cobalt manganese oxide ternary material; the two or more kinds of lithium nickel cobalt manganese oxide ternary material are divided into two groups, the chemical formula of the first group of lithium nickel cobalt manganese oxide ternary material is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, and 0.15≤y1≤0.60 are satisfied; and the chemical formula of the second group of lithium nickel cobalt manganese oxide ternary material is Li n2 Ni x2 Co y2 Mn z2 M2 m2O2, x2+y2+z2+m2=1, satisfying 0

[0008] In an embodiment of the present application, the mass percentage of the first group of nickel-cobalt-manganese lithium ternary materials is a, and the mass percentage of the second group of nickel-cobalt-manganese lithium ternary materials is b, based on the total mass of the nickel-cobalt-manganese lithium ternary materials, 10%≤a≤80%, and 20%≤b≤90%; preferably, 30%≤a≤60%, and 40%≤b≤70%; further preferably, 40%≤a≤60%, and 40%≤b≤60%. By adjusting the content of nickel-cobalt-manganese lithium ternary materials with different cobalt contents within the scope of the present application, the discharge performance of NCM lithium batteries at low temperature and low SOC state can be improved.

[0009] In an embodiment of the present application, the nickel-cobalt-manganese lithium ternary material can include a doping or coating element, and M1 and M2 are each independently selected from at least one of Ag, Sn, Zn, Al, Mo, Cu, B, Ti, and Fe. The addition of the above-mentioned doping or coating element in the positive electrode active material can make the conductive network on the surface of the positive electrode active material particles more dense 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 beneficial to form a passivation film on the surface of the positive electrode active material particles, thereby improving the initial 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 O2, m1 and m2 can be 0, i.e., the nickel-cobalt-manganese ternary material can also not include a doping or coating element.

[0010] In an embodiment of the present application, the two or more nickel-cobalt-manganese lithium ternary materials are divided into two groups according to the value of y, the first group of nickel-cobalt-manganese lithium ternary materials satisfies 0.15≤y1≤0.50, and the second group of nickel-cobalt-manganese lithium ternary materials satisfies 0.02≤y2≤0.10. By adjusting the cobalt atom mole content of the nickel-cobalt-manganese lithium ternary material within the scope of the present application, the impedance of the battery can be reduced, the battery discharge voltage platform can be stabilized, and the low-temperature discharge time of the battery can be prolonged.

[0011] In an embodiment of the present application, the particle size of the first group of nickel-cobalt-manganese lithium ternary materials is D V150, 1 μm≤D V1 50≤10 μm, preferably, 2 μm≤D V1 50≤9 μm. By regulating the particle size of the nickel cobalt manganese lithium material within the scope of the present application, the distance of lithium ion transmission during battery charging and discharging can be improved, thereby prolonging the discharge time of the battery in a low temperature environment.

[0012] In an embodiment of the present application, the particle size of the second group of nickel cobalt manganese lithium ternary materials is D V2 50, 1 μm≤D V2 50≤15 μm, optionally, 2 μm≤D V2 50≤10 μm. By regulating the particle size of the nickel cobalt manganese lithium material within the scope of the present application, the distance of lithium ion transmission during battery charging and discharging can be improved, thereby prolonging the discharge time of the battery in a low temperature environment.

[0013] In an embodiment of the present application, the chemical formula of the first group of nickel cobalt manganese lithium ternary materials is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, wherein, 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 lithium ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, wherein, 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, 0≤m2≤0.2.

[0014] In an embodiment of the present application, the positive electrode active material includes two kinds of nickel cobalt manganese lithium ternary materials NCM-1 and NCM-2, NCM-1 satisfies: 0.15≤y1≤0.60, and NCM-2 satisfies: 0<y2≤0.14. By regulating the range of the cobalt content y of the nickel cobalt manganese lithium ternary material within the scope of the present application, preferably using two kinds of nickel cobalt manganese lithium ternary materials, the battery impedance can be reduced while the battery discharge voltage platform is improved, thereby improving the discharge capacity of the battery in a low temperature environment.

[0015] In an embodiment of the present application, the positive electrode material layer further comprises an electrically conductive agent and a binder, the material of the electrically conductive agent is selected from at least one of electrically conductive carbon black and carbon nanotubes, and the material of 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 hydroxymethyl cellulose, and potassium hydroxymethyl cellulose.

[0016] In an embodiment of the present application, the mass percentage of the electrically 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] The second aspect of the present application provides a method for preparing the electrochemical device in any of the foregoing embodiments.

[0018] The two or more than two kinds of lithium nickel cobalt manganese ternary materials are mixed to obtain a positive electrode active material; wherein the two or more than two kinds of lithium nickel cobalt manganese ternary materials used are divided into two groups, the chemical formula of the lithium nickel cobalt manganese ternary material in the first group is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, 0.15≤y1≤0.60 is satisfied, and the chemical formula of the lithium nickel cobalt manganese ternary material in the second group is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, and 0

[0019] The third aspect of the present application provides an electronic device comprising the electrochemical device in any of the foregoing embodiments.

[0020] The beneficial effects of the present application are as follows:

[0021] The present application provides an electrochemical device, which comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material, and the positive electrode active material comprises two or more than two kinds of lithium nickel cobalt manganese ternary materials, the two or more than two kinds of lithium nickel cobalt manganese ternary materials are divided into two groups, the chemical formula of the lithium nickel cobalt manganese ternary material in the first group is Li n1 Ni x1 Co y1 Mnz1 M1 m1 O2, x1+y1+z1+m1=1, 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, 0

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

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

[0024] It should be noted that in the specific embodiments of the present application, lithium ion batteries are used as examples of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium ion batteries. The specific technical solutions are as follows:

[0025] The present application provides an electrochemical device, the electrochemical device comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, the positive electrode active material comprising two or more kinds of lithium nickel cobalt manganese oxide ternary materials, wherein the lithium nickel cobalt manganese oxide ternary material is a layered structure. The chemical formula of the lithium 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 amount of cobalt atoms in the lithium nickel cobalt manganese oxide ternary material is y, and the two or more kinds of lithium 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 lithium nickel cobalt manganese oxide ternary materials is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, 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 Mnz2 M2 m2 O2, x2+y2+z2+m2=1, satisfying 0

[0026] The inventors have found that when the nickel-cobalt-manganese lithium acid ternary material is used as a positive active material, it quickly reaches the discharge cut-off voltage (3.0 V) at low temperature and low SOC, and the low temperature and low SOC discharge performance is significantly deteriorated, which is difficult to meet the actual product application requirements. Generally, lithium cobaltate material is used to replace the nickel-cobalt-manganese lithium acid ternary material, which can meet the discharge performance requirements at low temperature and low SOC, but the lithium cobaltate material consumes relatively low cobalt metal resources, and the cost is high, which is not conducive to reducing the cost of the battery. When the content of cobalt element in the nickel-cobalt-manganese lithium acid ternary material is relatively high (for example, 0.15≤y≤0.60), the discharge voltage of the ternary material is lower, and the discharge curve is smoother; when the content of cobalt element in the nickel-cobalt-manganese lithium acid ternary material is relatively low (for example, 0

[0027] The mass percentage of the first group of nickel-cobalt-manganese lithium ternary materials is a, and the mass percentage of the second group of nickel-cobalt-manganese lithium 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%. Exemplarily, a can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range formed by 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 formed by any two of the above values. After mixing two or more kinds of nickel-cobalt-manganese lithium ternary materials, by adjusting the mass percentages a and b (for example, a=80%, b=20%) of the two kinds of nickel-cobalt-manganese lithium ternary materials with high cobalt element content and low cobalt element content based on the total mass of the positive electrode active material, the mixed nickel-cobalt-manganese lithium ternary material can have a relatively flat discharge curve while having a high discharge voltage, so that by adjusting the types and contents of the nickel-cobalt-manganese lithium ternary materials within the above range, the discharge performance of the NCM lithium battery at low temperature and low SOC state can be improved.

[0028] In an embodiment of the present application, the nickel-cobalt-manganese lithium ternary material can include a doping or coating element, and 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 element to the positive electrode active material can make the conductive network on the surface of the positive electrode active material particle more dense and have better kinetic performance; on the other hand, it can reduce the specific surface area of the positive electrode active material, reduce the side reaction between the positive electrode active material and the electrolyte; on the other hand, it is beneficial to form a passivation film on the surface of the positive electrode active material particle, improve its initial 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 m1 and m2 in O2 can be 0, that is, the nickel-cobalt-manganese ternary material can also not include a doping or coating element.

[0029] In an embodiment of the present application, the particle size of the first group of nickel-cobalt-manganese lithium ternary materials is D V1 50, 1 μm≤D V150≤10μm, preferably, 2μm≤D V1 50≤9μm, exemplary, 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 aforementioned values. The particle size of the first group of lithium nickel cobalt manganese oxide ternary material is D V2 50, 1 μm≤D V2 50≤15μm, preferably, 2μm≤D V2 50≤10μm, exemplary, D V2 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, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or a range consisting of any two of the aforementioned values. The particle size of the lithium nickel cobalt manganese oxide ternary material affects the distance of lithium ion transmission during battery charging and discharging. The longer the transmission distance, the worse the discharge time at low temperature. By adjusting the particle size of the lithium nickel cobalt manganese oxide material within the scope of the present application, the distance of lithium ion transmission during battery charging and discharging can be improved, thereby prolonging the discharge time of the battery in a low temperature environment.

[0030] In an embodiment of the present application, the chemical formula of the first group of lithium nickel cobalt manganese oxide ternary material is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, wherein 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 material is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, wherein 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, 0≤m2≤0.2.

[0031] In an embodiment of the present application, the positive active material includes two kinds of lithium nickel cobalt manganese oxide ternary materials, which are divided into NCM-1 and NCM-2 according to the content of cobalt element y, 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 composed of any two of the above values; NCM-2 satisfies: 0

[0032] In the present application, the preparation method of the lithium nickel cobalt manganese oxide ternary material is not particularly limited, as long as the purpose of the present application can be achieved. For example, the following method can be used for preparation:

[0033] The nitrate, sulfate or chloride of Ni, Co and Mn is co-precipitated under the action of ammonia water or ammonium bicarbonate complexing agent to prepare NCM carbonate or hydroxide precursor, and then the precursor is high-temperature sintered with lithium hydroxide or lithium carbonate at 700-1000°C to obtain the lithium nickel cobalt manganese oxide ternary material.

[0034] In the present application, the positive 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 nanotube, for example, the conductive carbon black can include but is not limited to at least one of acetylene black or ketjen black, and the carbon nanotube can include but is not limited to single-walled carbon nanotube and / or multi-walled carbon nanotube. The material of 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 hydroxymethyl cellulose and potassium hydroxymethyl cellulose.

[0035] In an embodiment of the present application, the mass percentage of the conductive agent is 1% to 8% based on the mass of the positive electrode material layer, and the mass percentage of the conductive agent may, for example, 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 defined by any two of the above values. The mass percentage of the binder is 1% to 3%, and the mass percentage of the binder may, for example, be 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3%, or a range defined by any two of the above values. By adjusting the types and contents of the conductive agent and the binder within the above ranges, the discharge performance of the NCM lithium battery at low temperature and low SOC can be improved.

[0036] The positive electrode tab of the present application also includes a positive electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, and may, for example, include an aluminum foil, an aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector), etc.

[0037] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in the present application as long as the purpose of the present 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.

[0038] In the present application, the electrochemical device also includes a negative electrode tab, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "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 the thickness direction of the negative electrode current collector, or can be disposed on both surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the negative electrode current collector, or can be a partial area of the surface of the negative electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved.

[0039] The negative electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, and may, for example, include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, and may, for example, 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.

[0040] The negative material layer includes a negative active material, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the negative active material can include, but is not limited to, at least one of natural graphite, artificial graphite, meso-carbon microbead, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O12, or Li-Al alloy. 12 or Li-Al alloy.

[0041] In some embodiments of the present application, the negative material layer can further include a conductive agent and a binder, which are not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, they can be at least one of the conductive agent and the binder described above. The mass ratio of the negative active material, the conductive agent, and the binder in the negative material layer is not particularly limited in the present application, which can be selected by a person skilled in the art according to actual needs as long as the purpose of the present application can be achieved.

[0042] The thickness of the negative material layer is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the negative material layer is 30 μm to 120 μm.

[0043] The thickness of the negative current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the negative current collector is 4 μm to 15 μm.

[0044] Optionally, the negative electrode sheet can further include a conductive layer, which is located between the negative current collector and the negative material layer. The composition of the conductive layer is not particularly limited in the present application, which can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, which can be at least one of the conductive agent and the binder described above.

[0045] In the present application, the electrochemical device further includes a separator. The separator is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film, or spunlaced film.

[0046] In some embodiments of the present application, the separator can include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer can 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 can be used.

[0047] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0048] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited in the present application, and for example, the inorganic particles can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder is not particularly limited in the present application, and 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 a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0049] 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, and for example, the thickness of the separator can be 3 μm to 30 μm.

[0050] The second aspect of the present application provides a method for preparing an electrochemical device according to any one of the preceding embodiments. Two or more than two lithium nickel cobalt manganese oxide ternary materials are mixed to obtain a positive electrode active material; wherein the two or more than two lithium nickel cobalt manganese oxide ternary materials used are divided into two groups, the chemical formula of the lithium nickel cobalt manganese oxide ternary material in the first group is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, 0.15≤y1≤0.60 is satisfied, and the chemical formula of the lithium nickel cobalt manganese oxide ternary material in the second group is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, 0 The positive electrode active material is arranged on at least one surface in the thickness direction of the positive electrode current collector to obtain a positive electrode sheet.

[0051] The third aspect of the present application provides an electronic device comprising the electrochemical device of any of the preceding embodiments. The electronic device provided by the present application has good use performance. The present application does not particularly limit the type of the electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0052] Embodiments

[0053] Hereinafter, embodiments and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, “parts” and “%” are on a mass basis.

[0054] Test methods and apparatus:

[0055] Cobalt element content test:

[0056] Using a scanning electron microscope (SEM), selected NCM material particles were subjected to element type analysis using an energy dispersive spectrometer (EDS). It should be noted that the mass of each element is obtained using the EDS test, and if the number of moles of atoms of each element is desired, the following formula needs to be used for conversion: n’ = m’ / M’, where n’ is the number of moles of atoms of each element, m’ is the mass of each element measured using EDS, and M’ is the molar mass of each element. Thus, the number of moles of cobalt atoms in the lithium nickel cobalt manganese ternary material is n’(Co) = m’(Co) / M’(Co).

[0057] Test of content of each component in the positive electrode active material layer:

[0058] The prepared positive electrode sheet was subjected to oxygen passage high temperature calcination at 500°C for 4 hours to remove the carbon-containing conductive agent and organic binder components in the sheet. The powder after high temperature treatment was uniformly dispersed in water, 1 mL of the suspension was taken and dried to prepare a sample, SEM and EDS were used for observation, 1000 times magnification was used for observation, the composition and particle number of all NCM particles in a random field were counted, and the content of each component was counted according to the composition and particle number.

[0059] Particle size test:

[0060] The suspension is dried to prepare a sample, and when observed by SEM and EDS, in addition to counting the components and the number of particles, the particle size is counted to obtain the Dv50 of different components.

[0061] Low-temperature discharge performance test

[0062] Low-temperature low-SOC discharge test of the battery: the battery is discharged at 0.2C discharge rate to 3.0V, and then charged at 0.2C rate for 0.5H. The battery is placed in a low-temperature condition of 0°C, and discharged at 1C and 0.5C rates, respectively. The duration of discharging to 3.0V is recorded.

[0063] Example 1-1

[0064] Preparation of the positive electrode sheet

[0065] LiNi 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 are 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-methyl pyrrolidone (NMP) is added as a solvent, and a slurry with a solid content of 75wt% is prepared, and stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and the coating weight of the positive electrode active material layer on the positive electrode sheet is 180g / m 2 , and dried at 90°C to obtain a positive electrode sheet coated with a single-sided positive electrode active material layer. Then the above steps are repeated on the other surface of the aluminum foil, and a positive electrode sheet coated with a double-sided positive electrode active material layer is obtained. After coating, the positive electrode sheet is cold-pressed, and the compaction density is 4.1g / cm 3 . Then the sheet is cut and the tabs are welded to obtain a positive electrode sheet with a size of 74mm×867mm.

[0066] Preparation of the negative electrode sheet

[0067] The negative active material artificial graphite, conductive carbon black (Super P), and polyacrylic acid were mixed in a weight ratio of 97.3:1.5:1.2, deionized water (H2O) was added as a solvent, and a slurry with a solid content of 70 wt% was prepared and stirred uniformly to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on one surface of a negative current collector copper foil with a thickness of 10 μm, and the coating weight of the negative active material layer on the negative electrode tab was 95 g / m 2 , and dried at 110°C to obtain a negative electrode tab coated with a single-sided negative active material layer. Then the above steps were repeated on the other surface of the copper foil to obtain a negative electrode tab coated with a double-sided negative active material layer. After coating, the negative electrode tab was cold-pressed to a compaction density of 1.7 g / cm 3 . After cutting and welding the tabs, a negative electrode tab with a size of 78 mm x 875 mm was obtained for use. The Dv50 of the negative active material artificial graphite was 10 μm, and the specific surface area was 1.6 m 2 / g by adjusting the ball milling time.

[0068] <Preparation of electrolyte>

[0069] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC: EMC: DEC = 3:5:2 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added to the above base solvent to obtain an electrolyte. The mass percentage of lithium salt based on the mass of the electrolyte was 12.5%, and the remainder was the base solvent.

[0070] <Separator>

[0071] A polyethylene film with a thickness of 9 μm was selected as the separator.

[0072] <Preparation of lithium ion battery>

[0073] The positive electrode tab, the separator, and the negative electrode tab were stacked in order, with the separator between the positive electrode tab and the negative electrode tab to act as a separator, and then wound to obtain an electrode assembly; the electrode assembly was placed in an outer packaging foil, and then the above prepared electrolyte was injected, and then subjected to processes such as formation, degassing, and edge cutting to obtain a lithium ion battery.

[0074] Examples 1-2 to 1-32

[0075] Except for changing the preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0076] Example 1-33

[0077] LiNi0.5 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 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) as a solvent, and mixed to a solid content of 75wt% to obtain a cathode slurry. The cathode slurry was uniformly coated on one surface of a cathode current collector aluminum foil having a thickness of 10μm, and the coated weight of the cathode active material layer on the cathode electrode sheet was 180g / m 2 , and dried at 90℃ to obtain a cathode electrode sheet coated with a single cathode active material layer on one surface. The rest was the same as Example 1-1, and a low-temperature discharge performance test was performed.

[0078] Example 1-34

[0079] LiNi 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 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) as a solvent, and mixed to a solid content of 75wt% to obtain a cathode slurry. The cathode slurry was uniformly coated on one surface of a cathode current collector aluminum foil having a thickness of 10μm, and the coated weight of the cathode active material layer on the cathode electrode sheet was 180g / m 2 , and dried at 90℃ to obtain a cathode electrode sheet coated with a single cathode active material layer on one surface. The rest was the same as Example 1-1, and a low-temperature discharge performance test was performed.

[0080] Example 1-35

[0081] LiNi0.5 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 with conductive carbon black (Super P), CNT and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.5:1.0:1.0:1.5, then N-methyl pyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%, and the slurry was stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and the coating weight of the positive active material layer on the positive electrode tab was 180g / m 2 , and dried at 90℃ to obtain a positive electrode tab with a single-sided coated positive active material layer. The rest was the same as Example 1-1, and a low-temperature discharge performance test was performed.

[0082] Comparative Example 1

[0083] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0084] Table 2

[0085] As can be seen from Examples 1-1 to 1-11 and Comparative Example 1, by adjusting the content y1, y2 of cobalt element in the two groups of lithium nickel cobalt manganese ternary materials within the scope of the present application, the discharge time of the secondary battery under 0℃ low-temperature conditions at 1C and 0.5C rate is improved, thereby indicating that the discharge performance of the lithium ion battery under low-temperature and low-SOC state is improved. According to the discharge time of Examples 1-1 to 1-11 under 0℃ low-temperature conditions at 1C and 0.5C rate, the content y1, y2 of cobalt element has a preferred range.

[0086] The mass percentage of the two groups of nickel-cobalt-manganese lithium ternary materials based on the total mass of the positive electrode active material affects the low-temperature discharge performance of the secondary battery. As can be seen from Example 1-1, Examples 1-12 to 1-16, and Examples 1-31 and 1-32, by adjusting the mass percentages a and b of the two groups of nickel-cobalt-manganese lithium ternary materials to satisfy 10%≤a≤80% and 20%≤b≤90%, the discharge time of the secondary battery under 0°C low-temperature conditions at 1C and 0.5C rates is improved, thereby indicating that the discharge performance of the lithium ion battery under low-temperature and low-SOC conditions is improved. As can be seen from the discharge time of Example 1-1, Examples 1-12 to 1-16, and Examples 1-31 and 1-32 under 0°C low-temperature conditions at 1C and 0.5C rates, the mass percentages a and b of the nickel-cobalt-manganese lithium ternary material show a trend of first increasing and then decreasing as a increases, thereby indicating that the mass percentages a and b of the nickel-cobalt-manganese lithium ternary material have an optimal range, 30%≤a≤60% and 40%≤b≤70%. Further, a and b have a more optimal range, 40%≤a≤60% and 40%≤b≤60%.

[0087] The particle size of the two groups of nickel-cobalt-manganese lithium ternary materials affects the low-temperature discharge performance of the secondary battery. As can be seen from Example 1-1, Examples 1-17 to 1-28, and Comparative Example 1, by adjusting the particle size D V1 50 and D V2 50 of the two groups of nickel-cobalt-manganese lithium ternary materials within the scope of the present application, the discharge time of the secondary battery under 0°C low-temperature conditions at 1C and 0.5C rates is improved, thereby indicating that the discharge performance of the lithium ion battery under low-temperature and low-SOC conditions is improved. As can be seen from the discharge time of Example 1-1, Examples 1-17 to 1-28 under 0°C low-temperature conditions at 1C and 0.5C rates, the particle size D V1 50 of the nickel-cobalt-manganese lithium ternary material has a greater effect on the discharge time, and the particle size D V2 50 has a smaller effect, thereby indicating that the particle size of the cobalt-manganese ternary material has an optimal range.

[0088] The content of the conductive agent affects the low-temperature discharge performance of the secondary battery. As can be seen from Example 1-1, Examples 1-29 and 1-30, and Comparative Example 1, by adjusting the content of the conductive agent within the scope of the present application, the discharge time of the secondary battery under 0°C low-temperature conditions at 1C and 0.5C rates is improved, thereby indicating that the discharge performance of the lithium ion battery under low-temperature and low-SOC conditions is improved.

[0089] The secondary batteries prepared by mixing two or more kinds of lithium nickel cobalt manganese oxide ternary materials are shown in Table 2. As can be seen from Example 1-1 and Examples 1-33 to 1-35 and Comparative Example 1, by adjusting the types and contents of two or more kinds of lithium nickel cobalt manganese oxide ternary materials within the scope of the present application, the discharge time of the secondary batteries at 0 ℃ low temperature condition at 1C and 0.5C rate is improved. Comparative Example 1-33 and Example 1-1, Example 1-33 increases a group of high cobalt content (0.15≤y≤0.60) ternary materials, the cobalt content is increased, which reduces the discharge voltage platform and improves the material impedance, and the discharge performance is improved; Comparative Example 1-34 and Example 1-1, Example 1-34 increases a group of low cobalt content (0

[0090] The above description is merely preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle 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, the positive electrode sheet 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 than two lithium nickel cobalt manganese ternary materials; the two or more than two lithium nickel cobalt manganese ternary materials are divided into two groups, the chemical formula of the first group of lithium nickel cobalt manganese ternary materials is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, 0.15<=y1<=0.60, and the chemical formula of the second group of lithium nickel cobalt manganese ternary materials is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, and 0 2. The electrochemical device of claim 1, wherein, The mass percentage of the first group of nickel-cobalt-manganese lithium ternary materials is a, and the mass percentage of the second group of nickel-cobalt-manganese lithium ternary materials is b, 10%≤a≤80%, and 20%≤b≤90%, based on the total mass of the nickel-cobalt-manganese lithium ternary materials.

3. The electrochemical device of 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%, and 40%≤b≤70%.

5. The electrochemical device of claim 4, wherein, 40%≤a≤60%, and 40%≤b≤60%.

6. The electrochemical device according to any one of claims 1 to 5, wherein, 0.15≤y1≤0.50, and 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 lithium nickel cobalt manganese oxide ternary material is D V1 50, 1 μm≤D V1 50≤10 μm.

8. The electrochemical device of claim 7, wherein, 2 μm < D V1 50 < 9 μm.

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

10. The electrochemical device of claim 9, wherein, 2 μm < D V2 50 < 10 μm.

11. The electrochemical device of claim 1, wherein, 0.95≤n1≤1.05, 0.3≤x1≤0.84, 0.01≤z1≤0.7, and 0≤m1≤0.2; 0.95≤n2≤1.05, 0.3≤x2≤0.9, 0.01≤z2≤0.7, and 0≤m2≤0.

2.

12. The electrochemical device of claim 1, wherein, The positive active material includes two nickel-cobalt-manganese lithium 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 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, and the material of 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 hydroxymethyl cellulose, and potassium hydroxymethyl cellulose.

14. The electrochemical device of claim 13, wherein, 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 material layer.

15. A preparation method of the electrochemical device according to any one of claims 1 to 14, comprising: The positive electrode sheet is prepared: the two or more than two kinds of nickel cobalt lithium manganate ternary materials are mixed to obtain the positive electrode active material; wherein the two or more than two kinds of nickel cobalt lithium manganate ternary materials used are divided into two groups, the chemical formula of the first group of nickel cobalt lithium manganate ternary material is Li n1 Ni x1 Co y1 Mn z1 M1 m1 O2, x1+y1+z1+m1=1, 0.15≤y1≤0.60 is satisfied, and the chemical formula of the second group of nickel cobalt lithium manganate ternary material is Li n2 Ni x2 Co y2 Mn z2 M2 m2 O2, x2+y2+z2+m2=1, 0 The positive electrode active material is arranged on at least one surface of the positive electrode current collector in the thickness direction 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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