Lithium ion battery and application thereof

Abstract

The application provides a lithium ion battery and application thereof. Metal elements in a positive active layer of the lithium ion battery satisfy the following relations: when the charging cut-off voltage of the lithium ion battery at 100% state of charge is 4.45V, m>0.284 and n>1.8; or, when the charging cut-off voltage of the lithium ion battery at 100% state of charge is 4.48V, m>0.242 and n>2.3; or, when the charging cut-off voltage of the lithium ion battery at 100% state of charge is 4.50V, m>0.2145 and n>4.1; wherein, m is the molar ratio of lithium elements in the positive active layer to metal elements in the positive active layer; n is the molar ratio of lithium elements in the positive active layer to manganese elements in the positive active layer or the molar ratio of lithium elements in the positive active layer to nickel elements in the positive active layer. The lithium ion battery has high cycle performance at high voltage and is low in price.

Description

Technical Field

[0001] This invention relates to a lithium-ion battery and its application, belonging to the field of lithium-ion battery technology. Background Technology

[0002] Lithium-ion batteries are widely used in smart electronic products, large-scale energy storage power stations, and electric vehicles due to their advantages such as high specific capacity, long cycle life, no memory effect, and cleanliness. As human demand for batteries continues to increase, improving energy density, lifespan, safety performance, and reducing costs are gradually becoming the development direction for lithium-ion batteries.

[0003] Cathode materials are one of the key materials restricting the cost-effectiveness of lithium-ion batteries. Among them, lithium cobalt oxide has advantages such as high operating voltage and good rate performance, and is currently one of the most widely used cathode materials in commercial applications. However, with the gradual depletion of cobalt resources, the price of lithium cobalt oxide materials containing cobalt will increase. Currently, lithium cobalt oxide materials account for the largest proportion of the raw material cost of lithium-ion batteries, reaching more than 40% of the total, which will further increase the cost of lithium-ion batteries. Meanwhile, existing nickel-cobalt-manganese ternary materials have poor cycle performance and thermal stability at high voltages (≥4.45V) and high temperatures, making it difficult to meet the current demands for high voltage and high cycle performance in batteries.

[0004] Therefore, there is an urgent need to develop a high-voltage (≥4.45V) lithium-ion battery with high cycle performance and low cost. Summary of the Invention

[0005] This invention provides a lithium-ion battery that is not only inexpensive but also has good cycle performance under high voltage.

[0006] The present invention provides an electronic device whose driving source and / or energy storage source is not only inexpensive, but also has good cycle performance under high voltage.

[0007] This invention provides a lithium-ion battery, including a positive electrode sheet;

[0008] The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one functional surface of the positive current collector;

[0009] The positive electrode active layer includes a positive electrode active material, which includes lithium cobalt oxide and lithium nickel cobalt manganese oxide.

[0010] The metal elements in the positive electrode active layer satisfy the following relationship:

[0011] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, m > 0.284, n > 1.8; or,

[0012] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, m > 0.242, n > 2.3; or,

[0013] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, m > 0.2145, n > 4.1;

[0014] Wherein, m is the molar ratio of lithium to metal in the positive electrode active layer; n is the molar ratio of lithium to manganese in the positive electrode active layer or the molar ratio of lithium to nickel in the positive electrode active layer.

[0015] In the lithium-ion battery described above, the lithium nickel cobalt manganese oxide is a non-monocrystalline lithium nickel cobalt manganese oxide.

[0016] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, m > 0.284, n > 3; or,

[0017] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, m > 0.242, n > 4; or,

[0018] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, m > 0.216 and n > 7.

[0019] Wherein, n is the molar ratio of lithium to manganese in the positive electrode active layer.

[0020] In the lithium-ion battery described above, the lithium nickel cobalt manganese oxide is a monocrystalline lithium nickel cobalt manganese oxide.

[0021] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, m > 0.285, n > 1.8; or,

[0022] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, m > 0.242, n > 2.3; or,

[0023] When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, m > 0.214, n > 4.1;

[0024] Wherein, n is the molar ratio of lithium to nickel in the positive electrode active layer.

[0025] In the lithium-ion battery described above, the charging cut-off voltage at 100% state of charge is 4.45V, and the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (70-95):(5-30).

[0026] In the lithium-ion battery described above, the charging cutoff voltage at 100% state of charge is 4.48V, and the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (80-95):(5-20).

[0027] In the lithium-ion battery described above, the charging cut-off voltage at 100% state of charge is 4.50V, and the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (90-95):(5-10).

[0028] In the lithium-ion battery described above, the non-monocrystalline lithium nickel cobalt manganese oxide has the general formula LiNi. 0.5 Co 0.2- a Mn 0.3 A a O2;

[0029] Where 0 ≤ a ≤ 0.01;

[0030] A is selected from at least one of Al, Mg, Ti, Zr, Y, La, Sr, Tb, and Pr;

[0031] Optionally, the non-single-crystal lithium nickel cobalt manganese oxide D 50 Its size is 4–11 μm.

[0032] In the lithium-ion battery described above, the general formula of the single-crystal nickel-cobalt-manganese lithium oxide is LiNi. c Co b Mn 1-c-b O2;

[0033] Where 0.3≤c≤0.9, 0.1≤b≤0.4;

[0034] Optionally, the D of the single-crystal lithium nickel cobalt manganese oxide 50 The size is 3–10 μm.

[0035] In the lithium-ion battery described above, the lithium cobalt oxide has the general formula Li. x Co 1-y-z M y N z O2;

[0036] Where 0.95≤x≤1.05, 0≤y≤0.15, 0≤z≤0.15;

[0037] M is selected from at least one of Al, Mg, Ti and Zr;

[0038] N is selected from at least one of Al, Ti, Y, La, Sr, Tb, and Pr;

[0039] Optionally, the D of the lithium cobalt oxide 50 Its size is 9–18 μm.

[0040] The present invention provides an electronic device, wherein the driving source and / or energy storage source of the electronic device comprises a lithium-ion battery as described above.

[0041] The lithium-ion battery of the present invention comprises lithium cobalt oxide and lithium nickel cobalt manganese oxide as positive active materials in the positive active layer, and the metal elements in the positive active layer have a specific relationship under a certain charging cutoff voltage. The lithium-ion battery can achieve high cycle performance at high voltage and has low manufacturing cost. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] A first aspect of the present invention provides a lithium-ion battery, including a positive electrode;

[0044] The positive electrode includes a positive current collector and a positive active layer disposed on at least one functional surface of the positive current collector;

[0045] The positive electrode active layer includes positive electrode active materials, which include lithium cobalt oxide and lithium nickel cobalt manganese oxide;

[0046] The metal elements in the positive electrode active layer satisfy the following relationship:

[0047] When the charging cutoff voltage for a lithium-ion battery at 100% state of charge is 4.45V, m > 0.284, n > 1.8; or,

[0048] When the charging cutoff voltage for a lithium-ion battery at 100% state of charge is 4.48V, m > 0.242, n > 2.3; or,

[0049] When the charging cutoff voltage of a lithium-ion battery at 100% state of charge is 4.50V, m > 0.2145 and n > 4.1;

[0050] Where m is the molar ratio of lithium to metal in the positive electrode active layer; n is the molar ratio of lithium to manganese or lithium to nickel in the positive electrode active layer.

[0051] It is understood that the lithium-ion battery of the present invention includes a positive electrode sheet. It also includes a negative electrode sheet, a separator, an electrolyte, and an outer packaging. The lithium-ion battery of the present invention can be obtained by stacking the positive electrode sheet, the separator, and the negative electrode sheet, or by stacking the positive electrode sheet, the separator, and the negative electrode sheet, and then winding them. The battery is then placed in the outer packaging, and the electrolyte is injected into the outer packaging.

[0052] In this invention, the functional surface refers to the two surfaces with the largest area in the current collector that are arranged opposite each other.

[0053] The present invention can obtain a positive electrode sheet by setting a positive electrode active layer on one functional surface of the positive electrode current collector, or by setting a positive electrode active layer on two functional surfaces of the positive electrode current collector.

[0054] The positive electrode active layer of the present invention includes a positive electrode active material, which includes lithium cobalt oxide and lithium nickel cobalt manganese oxide.

[0055] In this invention, the molar ratio m of lithium to metal elements in the positive electrode active layer refers to the proportion of the amount of lithium in the positive electrode active layer to the total amount of metal elements in the positive electrode active layer, where metal elements include all metal elements in the positive electrode active layer; the molar ratio n of lithium to manganese in the positive electrode active layer or the molar ratio n of lithium to nickel in the positive electrode active layer refers to the proportion of the amount of lithium in the positive electrode active layer to the amount of manganese in the positive electrode active layer or the proportion of the amount of lithium in the positive electrode active layer to the amount of nickel in the positive electrode active layer.

[0056] In one embodiment, the lithium-ion battery can be charged to 100% state of charge at different charging cut-off voltages. Then, the lithium-ion battery is disassembled and the positive electrode is retained. Atomic absorption spectroscopy is used to test the amount of each metal element in the positive electrode active layer, and m and n are obtained by calculation.

[0057] The present invention does not impose any particular limitation on the specific structure of the negative electrode, the separator, and the outer packaging, nor does it impose any particular limitation on the specific composition of the electrolyte. The components can be selected from conventional negative electrode, separator, electrolyte, and outer packaging in the art.

[0058] For example, the present invention can form a negative electrode sheet by setting a negative electrode active layer on one functional surface of the negative electrode current collector, or by setting a negative electrode active layer on both functional surfaces of the negative electrode current collector.

[0059] In this invention, the negative electrode active layer comprises a negative electrode active material, a conductive agent, and a binder. In some embodiments, based on the total mass of the negative electrode active layer, the mass percentage of the negative electrode active material is 70-99%, the mass percentage of the conductive agent is 0.5-15%, and the mass percentage of the binder is 0.5-15%.

[0060] Furthermore, based on the total mass of the negative electrode active layer, the mass percentage of the negative electrode active material is 80-98%, the mass percentage of the conductive agent is 1-10%, and the mass percentage of the binder is 1-10%.

[0061] In this invention, the negative electrode active material can be selected from at least one of artificial graphite, hard carbon, natural graphite, lithium titanate, mesophase carbon microspheres, silicon suboxide, and silicon carbide.

[0062] The conductive agent can be selected from at least one of conductive carbon black, Ketjen black, acetylene black, conductive carbon fiber, conductive graphite, carbon nanotubes, graphene, conductive oxides, metal powder and carbon fiber.

[0063] The adhesive may be selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, and lithium polyacrylate.

[0064] The diaphragm in this invention can be a polypropylene diaphragm, a coated diaphragm with ceramic coated on one side of a polypropylene diaphragm, or a coated diaphragm with ceramic coated on both sides of a polypropylene diaphragm.

[0065] In this invention, the electrolyte may include a non-aqueous solvent, a conductive lithium salt, and additives.

[0066] The additive may be selected from at least one of nitrile compounds, 1,3-propenesulfonate lactone, and vinylene carbonate.

[0067] The non-aqueous solvent may be selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, and propyl acetate.

[0068] The conductive lithium salt can be selected from at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0069] The aforementioned nitrile compounds may be selected from at least one of dinitrile, butadionitrile, and 1,2-bis(cyanoethoxy)ethane.

[0070] In this invention, the positive electrode active material includes lithium cobalt oxide and lithium nickel cobalt manganese oxide. In addition, when the charging cutoff voltage of the lithium-ion battery is 4.45V, m > 0.284 and n > 1.8; or when the charging cutoff voltage of the lithium-ion battery is 4.48V, m > 0.242 and n > 2.3; or when the charging cutoff voltage of the lithium-ion battery is 4.50V, m > 0.2145 and n > 4.1.

[0071] The lithium-ion battery of the present invention only needs to satisfy one of the three correspondences between the charging cut-off voltage and m and n, and a lithium-ion battery that simultaneously satisfies any two of the above-mentioned correspondences between the charging cut-off voltage and m and n, or a lithium-ion battery that simultaneously satisfies all three of the above-mentioned correspondences between the charging cut-off voltage and m and n, is also within the protection scope of the present invention.

[0072] It is understood that, in this invention, regardless of the number of charge-discharge cycles performed on the lithium-ion battery or the rate of charge-discharge cycles, as long as the charging cut-off voltage of the lithium-ion battery at 100% state of charge satisfies the specific correspondence between m and n as described above, it falls within the scope of protection of this invention.

[0073] According to the solution provided by the present invention, by limiting the composition of the positive electrode active material and the values ​​of m and n at different charging cutoff voltages, not only can the cost of lithium-ion batteries be reduced, but also the lithium-ion batteries can have higher cycle performance.

[0074] Specifically, lithium nickel cobalt manganese oxide (LCO) has a low cost, and its use can reduce the production cost of lithium-ion batteries.

[0075] Furthermore, the inventors analyzed the principle behind the improved cycle performance of lithium-ion batteries under high voltage, suggesting that when m and n have specific values ​​at a given charging cutoff voltage, the compatibility between lithium cobalt oxide and lithium nickel cobalt manganese oxide in the positive electrode active material is optimized. This allows for the full utilization of the advantages of lithium cobalt oxide and lithium nickel cobalt manganese oxide while minimizing their disadvantages, thereby achieving a lithium-ion battery with improved cycle performance under high voltage. Therefore, in the application of the lithium-ion battery of this invention, to ensure maximum cycle performance, the charging cutoff voltage of the lithium-ion battery should satisfy the corresponding charging cutoff voltage.

[0076] It is worth mentioning that because m and n have specific values ​​at a specific charging cutoff voltage, the lithium-ion battery of this invention exhibits high cycle performance under high voltage, and the manufacturing cost of this lithium-ion battery is low. Therefore, based on m and n of the lithium-ion battery at a specific charging cutoff voltage, the performance of the lithium-ion battery can be quickly obtained, and the performance of the positive electrode can be inferred, which can greatly shorten the evaluation cycle of the positive electrode active material and accelerate the development progress of the positive electrode active material.

[0077] The present invention does not limit the morphology of lithium nickel cobalt manganese oxide; it can be either monocrystalline or non-monocrystalline.

[0078] When lithium nickel cobalt manganese oxide is a non-single-crystal type, for example, the general formula is LiNi. 0.5 Co 0.2- a Mn 0.3 A a O2;

[0079] Where 0 ≤ a ≤ 0.01;

[0080] A is selected from at least one of Al, Mg, Ti, Zr, Y, La, Sr, Tb, and Pr.

[0081] Optionally, non-monocrystalline lithium nickel cobalt manganese oxide D 50 Its size is 4–11 μm.

[0082] In some embodiments, the molecular formula of non-single-crystal lithium nickel cobalt manganese oxide is LiNi. 0.5 Co 0.199 Mn 0.3 Al 0.001 O2 (non-monocrystalline NCM523).

[0083] When lithium nickel cobalt manganese oxide is a single-crystal type, for example, the general formula is:

[0084] LiNi c Co b Mn 1-c-b O2;

[0085] Where 0.3≤c≤0.9, 0.1≤b≤0.4.

[0086] Optionally, the D of single-crystal lithium nickel cobalt manganese oxide 50 The size is 3–10 μm.

[0087] In some embodiments, the molecular formula of single-crystal lithium nickel cobalt manganese oxide is LiNi. 0.5 Co 0.2 Mn 0.3 O2 (single-crystal NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) or LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811).

[0088] Furthermore, the inventors discovered that when using non-monocrystalline lithium nickel cobalt manganese oxide, the cycle performance of lithium-ion batteries can be improved by further limiting m and n.

[0089] Specifically, when the charging cutoff voltage at 100% state of charge is 4.45V, m > 0.284, n > 3; or, when the charging cutoff voltage at 100% state of charge is 4.48V, m > 0.242, n > 4; or, when the charging cutoff voltage at 100% state of charge is 4.50V, m > 0.216, n > 7; where n is the molar ratio of lithium to manganese in the positive electrode active layer. In this case, the lithium-ion battery of the present invention, including non-monocrystalline nickel-cobalt-manganese lithium oxide, exhibits superior cycle performance.

[0090] Furthermore, the inventors discovered that when using monocrystalline nickel-cobalt-manganese lithium oxide, further limiting m and n results in better cycle performance of the lithium-ion battery.

[0091] Specifically, when the charging cutoff voltage at 100% state of charge is 4.45V, m > 0.285 and n > 1.8; or, when the charging cutoff voltage at 100% state of charge is 4.48V, m > 0.242 and n > 2.3; or, when the charging cutoff voltage at 100% state of charge is 4.50V, m > 0.214 and n > 4.1; where n is the molar ratio of lithium to nickel in the positive electrode active layer. In this case, the lithium-ion battery of the present invention, including monocrystalline nickel-cobalt-manganese lithium oxide, exhibits superior cycle performance.

[0092] As an alternative implementation, the above-mentioned relationship between the charging cutoff voltage and m and n can be achieved by controlling the mass ratio of lithium cobalt oxide and lithium nickel cobalt manganese oxide, thereby achieving excellent cycle performance of lithium-ion batteries.

[0093] In some embodiments, the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (70-95):(5-30). When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, m and n meet the above range, thus the lithium-ion battery exhibits excellent cycle performance.

[0094] In some embodiments, the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (80-95):(5-20). When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, m and n meet the above range, thus the lithium-ion battery exhibits excellent cycle performance.

[0095] In some embodiments, the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (90-95):(5-10). When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, m and n meet the above range, thus the lithium-ion battery exhibits excellent cycle performance.

[0096] In some embodiments of the present invention, lithium cobalt oxide has the general formula Li. x Co 1-y-z M y N z O2;

[0097] Where 0.95≤x≤1.05, 0≤y≤0.15, 0≤z≤0.15;

[0098] M is selected from at least one of Al, Mg, Ti and Zr;

[0099] N is selected from at least one of Al, Ti, Y, La, Sr, Tb and Pr.

[0100] In practical applications, because the molecular formula is LiCo 0.983 Al 0.015 Mg 0.001 Ti 0.001 Lithium cobalt oxide with O2 exhibits more stable performance at a charging cutoff voltage of 4.45V, thus making it suitable for applications including LiCo. 0.983 Al 0.015 Mg 0.001 Ti 0.001 In the application of the lithium-ion battery of the present invention, the more suitable charging cutoff voltage for the lithium-ion battery is 4.45V. At this voltage, the mass ratio can be controlled to ensure that the lithium-ion battery meets the above-mentioned m and n at 4.45V, thereby significantly improving the cycle performance of the lithium-ion battery and achieving superior cycle performance. Since the molecular formula is LiCo... 0.973 Al 0.025 Mg 0.001 Ti 0.001 Lithium cobalt oxide with O2 exhibits more stable performance at a charging cutoff voltage of 4.48V, thus making it suitable for applications including LiCo. 0.973 Al 0.025 Mg 0.001 Ti 0.001 In the application of the lithium-ion battery of the present invention, the more suitable charging cutoff voltage for the lithium-ion battery is 4.48V. At this voltage, the mass ratio can be controlled to ensure that the lithium-ion battery meets the above-mentioned m and n at 4.48V, thereby giving the lithium-ion battery better cycle performance. Since the molecular formula is LiCo... 0.968 Al 0.03 Mg 0.001 Ti 0.001 Lithium cobalt oxide with O2 exhibits more stable performance at a charging cutoff voltage of 4.5V, thus making it suitable for applications including LiCo. 0.968 Al 0.03 Mg 0.001 Ti 0.001In the application of the lithium-ion battery of the present invention, the more suitable charging cutoff voltage for the lithium-ion battery is 4.5V. At this time, by controlling the mass ratio, the lithium-ion battery can meet the above-mentioned m and n at 4.5V, thereby enabling the lithium-ion battery to have better cycle performance.

[0101] Furthermore, the D of lithium cobalt oxide 50 Its size is 9–18 μm.

[0102] In some embodiments of the present invention, in order to further improve the cycle performance of lithium-ion batteries under high voltage and reduce the production cost of lithium-ion batteries, the positive electrode active layer also includes a conductive agent and a binder.

[0103] Based on the total mass of the positive electrode active layer, the mass percentage of the positive electrode active material is 70-99%, the mass percentage of the conductive agent is 0.5-15%, and the mass percentage of the binder is 0.5-15%.

[0104] Furthermore, based on the total mass of the positive electrode active layer, the mass percentage of the positive electrode active material is 80-98%, the mass percentage of the conductive agent is 1-10%, and the mass percentage of the binder is 1-10%.

[0105] A second aspect of the present invention provides an electronic device whose driving source and / or energy storage source includes the lithium-ion battery described above.

[0106] The aforementioned lithium-ion batteries can be used as power sources for electronic devices, or as energy storage units for electronic devices. These electronic devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, and energy storage systems.

[0107] Because this electronic device includes the aforementioned lithium-ion battery, it has a long service life under high voltage.

[0108] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0109] Example 1

[0110] The lithium-ion battery in this embodiment is prepared by a method including the following steps.

[0111] 1) Positive electrode plate

[0112] The positive electrode active material (composed of lithium cobalt oxide and lithium nickel cobalt manganese oxide), conductive agent Super-P, and binder polyvinylidene fluoride are dispersed in N-methylpyrrolidone (NMP) and stirred evenly to obtain a positive electrode active slurry. The positive electrode active slurry is uniformly coated on two functional surfaces of an aluminum foil. The aluminum foil coated with the positive electrode active slurry is placed in an oven at 100°C and baked for 8 hours. It is then rolled to form a positive electrode active layer, thus obtaining a positive electrode sheet.

[0113] The mass ratio of the positive electrode active material, conductive agent, and binder is 97%:1.5%:1.5%.

[0114] The mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is 95:5;

[0115] The molecular formula of lithium cobalt oxide is LiCo 0.983 Al 0.015 Mg 0.001 Ti 0.001 O2, D 50 The thickness is 9–18 μm;

[0116] The molecular formula of lithium nickel cobalt manganese oxide is LiNi 0.5 Co 0.199 Mn 0.3 Al 0.001 O2 (non-monocrystalline NCM523), D 50 The size is 4–11 μm;

[0117] The compaction density of the positive electrode active layer is 4.0 g / cm³. 3 .

[0118] 2) Negative electrode plate

[0119] Artificial graphite, superconducting carbon black (Super-P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are mixed with deionized water to prepare a negative electrode active slurry. The negative electrode active slurry is coated on two functional surfaces of an 8μm copper foil, then dried and rolled to obtain a negative electrode active layer, thus obtaining a negative electrode sheet.

[0120] The baking temperature was 100℃, and the baking time was 4 hours.

[0121] The compaction density of the negative electrode active layer is 1.65 g / cm³. 3 ;

[0122] The D50 of artificial graphite is 13±1μm, and the degree of graphitization is 94±0.5%. Artificial graphite is a mixture of secondary and single-particle graphite, with secondary particles accounting for 50% of the mass.

[0123] The mass ratio of artificial graphite, superconducting carbon black (Super-P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) is 96.4%:2%:0.8%:0.8%.

[0124] 3) Lithium-ion batteries

[0125] After stacking the positive electrode sheet and separator from step 1) and the negative electrode sheet from step 2), the cells are wound together to obtain a battery cell. The battery cell is then placed in an aluminum-plastic film for encapsulation. In a nitrogen-protected oven, the temperature is controlled at 120°C and baked for 36 hours. Electrolyte is injected into the aluminum-plastic film, and then the processes of chemical composition and sorting are carried out to finally obtain a soft-pack lithium-ion battery with a capacity of 5Ah.

[0126] The diaphragm consists of a ceramic layer and an oil-based LBG coating on two functional surfaces of a polypropylene substrate, and an oil-based LBG coating on the surface of the ceramic layer away from the polypropylene substrate.

[0127] The electrolyte was prepared by using LiPF6 as the lithium salt, a mixture of ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) as the solvent, and adding 4% 1,3-propenesulfonate lactone, 6% vinylene carbonate, 1% succinate, and 2% adiponitrile as additives.

[0128] Example 2

[0129] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 90:10.

[0130] Example 3

[0131] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0132] Example 4

[0133] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 80:20.

[0134] Example 5

[0135] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0136] Example 6

[0137] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 70:30.

[0138] Example 7

[0139] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 2, the only difference being that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.5 Co 0.2 Mn 0.3 O2 (single crystal type NCM523), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0140] Example 8

[0141] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 7. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 80:20.

[0142] Example 9

[0143] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 7. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 70:30.

[0144] Example 10

[0145] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, the only difference being that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.6 Co 0.2 Mn 0.2 O2 (NCM622), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0146] Example 11

[0147] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 10. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0148] Example 12

[0149] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 10. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0150] Example 13

[0151] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, the only difference being that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.8 Co0.1 Mn 0.1 O2 (NCM811), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0152] Example 14

[0153] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 13. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0154] Comparative Example 1

[0155] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 65:35.

[0156] Comparative Example 2

[0157] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 60:40.

[0158] Comparative Example 3

[0159] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 1. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 100:0.

[0160] Comparative Example 4

[0161] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 7, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 60:40.

[0162] Comparative Example 5

[0163] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 10, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 65:35.

[0164] Example 15

[0165] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, the only difference being that the chemical formula of lithium cobalt oxide in step 1) is LiCo. 0.973 Al 0.025 Mg 0.001 Ti 0.001 O2.

[0166] Example 16

[0167] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 90:10.

[0168] Example 17

[0169] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 16. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0170] Example 18

[0171] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 80:20.

[0172] Example 19

[0173] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 17, except that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.5 Co 0.2 Mn 0.3 O2 (single crystal type NCM523), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0174] Example 20

[0175] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 20. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 80:20.

[0176] Example 21

[0177] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 16, except that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.6 Co 0.2 Mn 0.2 O2 (NCM622), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0178] Example 22

[0179] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 22. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:15.

[0180] Example 23

[0181] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 16, except that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi.0.8 Co 0.1 Mn 0.1 O2 (NCM811), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0182] Comparative Example 6

[0183] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0184] Comparative Example 7

[0185] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 70:30.

[0186] Comparative Example 8

[0187] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 65:35.

[0188] Comparative Example 9

[0189] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 60:40.

[0190] Comparative Example 10

[0191] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 16, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 100:0.

[0192] Comparative Example 11

[0193] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 20, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 70:30.

[0194] Comparative Example 12

[0195] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 20, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 60:40.

[0196] Comparative Example 13

[0197] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 22, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0198] Comparative Example 14

[0199] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 22, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 65:35.

[0200] Comparative Example 15

[0201] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 24, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0202] Example 24

[0203] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 1, the only difference being that the chemical formula of lithium cobalt oxide in step 1) is LiCo. 0.968 Al 0.03 Mg 0.001 Ti 0.001 O2.

[0204] Example 25

[0205] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 26. The only difference is that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 90:10.

[0206] Example 26

[0207] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 27, except that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.5 Co 0.2 Mn 0.3 O2 (single crystal type NCM523), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0208] Example 27

[0209] The preparation steps of the lithium-ion battery in this embodiment are basically the same as those in Example 26, except that the molecular formula of lithium nickel cobalt manganese oxide in step 1) is LiNi. 0.6 Co 0.2 Mn 0.2 O2 (NCM622), the D50 of lithium nickel cobalt manganese oxide is 3-10μm.

[0210] Comparative Example 16

[0211] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0212] Comparative Example 17

[0213] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 80:20.

[0214] Comparative Example 18

[0215] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0216] Comparative Example 19

[0217] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 70:30.

[0218] Comparative Example 20

[0219] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 65:35.

[0220] Comparative Example 21

[0221] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 60:40.

[0222] Comparative Example 22

[0223] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 26, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 100:0.

[0224] Comparative Example 23

[0225] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 28, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 80:20.

[0226] Comparative Example 24

[0227] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 28, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 70:30.

[0228] Comparative Example 25

[0229] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 28, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 60:40.

[0230] Comparative Example 26

[0231] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 29, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0232] Comparative Example 27

[0233] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 29, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0234] Comparative Example 28

[0235] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 29, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 65:35.

[0236] Comparative Example 29

[0237] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 30, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 85:15.

[0238] Comparative Example 30

[0239] The preparation steps of the lithium-ion battery in this comparative example are basically the same as those in Example 30, except that the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide in step 1) is 75:25.

[0240] Performance testing

[0241] 1) Cyclic capacity retention

[0242] The lithium-ion batteries in the examples and comparative examples were charged and discharged at a constant temperature of 45°C at a rate of 1.0C / 1.0C. Under different charging cutoff voltage ranges, 500 charge-discharge cycles were performed. The discharge capacity of the first cycle and the discharge capacity of the 500-cycle cycle were recorded. The cycle capacity retention rate was obtained by dividing the discharge capacity of the 500-cycle cycle by the discharge capacity of the first cycle.

[0243] 2) Measurement of the amount of each metal element in the positive electrode active layer

[0244] The lithium-ion batteries of the examples and comparative examples were charged to 100% state of charge (SOC) at different charging cut-off voltages and then disassembled. After disassembly, the positive electrode was retained and immersed in a solution of dimethyl carbonate (DMC) for 30 minutes. After immersion, it was taken out and dried in an oven at 120°C for 6 hours.

[0245] The dried positive electrode sheet was placed in a tube furnace and sintered at high temperature. The tube furnace sintering temperature was set to 300℃ and the sintering time was set to 4h. After sintering, the positive electrode sheet was naturally cooled and placed in a sealed glass bottle.

[0246] Place the glass bottle containing the positive electrode sheet in an ultrasonic machine and sonicate for 15 minutes. After sonicating, remove the bottle and gently rub the surface of the positive electrode sheet to obtain positive electrode active layer powder in a 100% SOC state.

[0247] By using atomic absorption spectroscopy to test the above-mentioned positive electrode active layer powder, the amount of each metal element in the positive electrode active layer can be obtained.

[0248] Among them, the charging cut-off voltage range of the lithium-ion batteries in Examples 1-14 and Comparative Examples 1-5 during cycling is 3.0V to 4.45V; the charging cut-off voltage at 100% SOC is 4.45V. The relevant test results are shown in Table 1.

[0249] The charging cutoff voltage range of the lithium-ion batteries in Examples 15-23 and Comparative Examples 6-15 during cycling is 3.0V to 4.48V; the charging cutoff voltage at 100% SOC is 4.48V. The relevant test results are shown in Table 2.

[0250] The charging cutoff voltage range of the lithium-ion batteries in Examples 24-27 and Comparative Examples 16-30 during cycling is 3.0V to 4.50V; the charging cutoff voltage at 100% SOC is 4.5V. The relevant test results are shown in Table 3.

[0251] Table 1

[0252]

[0253]

[0254] Table 2

[0255]

[0256]

[0257] Table 3

[0258]

[0259]

[0260] As can be seen from Tables 1-3, the lithium-ion batteries of the present invention can achieve relatively excellent cycle performance.

[0261] Specifically, as can be seen from Table 1, compared with the lithium-ion battery of Comparative Example 3, the lithium-ion batteries of Examples 1-14 still maintain comparable cycle performance even with the reduction of lithium cobalt oxide content in the positive electrode active layer of Examples 1-14 (reduced production cost).

[0262] As can be seen from Table 2, compared with the lithium-ion battery of Comparative Example 8, the lithium-ion batteries of Examples 15-23 still maintain comparable cycle performance to those of Comparative Example 10, even with the reduction in lithium cobalt oxide content in the positive electrode active layer of Examples 15-23 (reduced production cost).

[0263] As can be seen from Table 3, compared with the lithium-ion battery of Comparative Example 22, the lithium-ion batteries of Examples 24-27 can still maintain comparable cycle performance even with the reduction of lithium cobalt oxide content in the positive electrode active layer of Examples 24-27 (reduced production cost).

[0264] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery, wherein the voltage of the lithium-ion battery is greater than or equal to 4.45V, characterized in that, Including the positive electrode plate; The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one functional surface of the positive current collector; The positive electrode active layer includes a positive electrode active material, which includes lithium cobalt oxide and lithium nickel cobalt manganese oxide; when the lithium nickel cobalt manganese oxide is a non-monocrystalline lithium nickel cobalt manganese oxide, the metal elements in the positive electrode active layer satisfy the following relationship: When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, m > 0.284, n > 3; or, When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, m > 0.242, n > 4; or, When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, m > 0.216, n > 7; Wherein, m is the molar ratio of lithium to metal in the positive electrode active layer; n is the molar ratio of lithium to manganese in the positive electrode active layer; When the lithium nickel cobalt manganese oxide is a single-crystal lithium nickel cobalt manganese oxide, the metal elements in the positive electrode active layer satisfy the following relationship: When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, m > 0.285, n > 1.8; or, When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, m > 0.242, n > 2.3; or, When the charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, m > 0.2163, n > 4.1; Wherein, m is the molar ratio of lithium to metal in the positive electrode active layer; n is the molar ratio of lithium to nickel in the positive electrode active layer; The general formula of the lithium cobalt oxide is Li x Co 1-y-z M y N z O2; Where 0.95≤x≤1.05, 0≤y≤0.15, 0≤z≤0.15; M is selected from at least one of Al, Mg, Ti and Zr; N is selected from at least one of Al, Ti, Y, La, Sr, Tb, and Pr.

2. The lithium-ion battery according to claim 1, characterized in that, The charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.45V, and the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (70~95):(5~30).

3. The lithium-ion battery according to claim 1, characterized in that, The charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.48V, and the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (80~95):(5~20).

4. The lithium-ion battery according to claim 1, characterized in that, The charging cutoff voltage of the lithium-ion battery at 100% state of charge is 4.50V, and the mass ratio of lithium cobalt oxide to lithium nickel cobalt manganese oxide is (90~95):(5~10).

5. The lithium-ion battery according to claim 1, characterized in that, The general formula of the non-single-crystal lithium nickel cobalt manganese oxide is LiNi. 0.5 Co 0.2-a Mn 0.3 A a O2; Where 0 ≤ a ≤ 0.01; A is selected from at least one of Al, Mg, Ti, Zr, Y, La, Sr, Tb, and Pr; The non-monocrystalline lithium nickel cobalt manganese oxide D 50 The value is 4~11μm.

6. The lithium-ion battery according to claim 1, characterized in that, The general formula of the single-crystal lithium nickel cobalt manganese oxide is LiNi c Co b Mn 1-c-b O2; Where 0.3≤c≤0.9, 0.1≤b≤0.4; The single-crystal lithium nickel cobalt manganese oxide D 50 The size is 3~10μm.

7. The lithium-ion battery according to any one of claims 1-6, characterized in that, The lithium cobalt oxide D 50 Its size is 9~18μm.

8. An electronic device, characterized in that, The driving source and / or energy storage source of the electronic device includes the lithium-ion battery according to any one of claims 1-7.

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