A positive electrode active material, a secondary battery, and an electrical device.

Abstract

This application relates to the field of battery technology, specifically to a positive electrode active material, a secondary battery, and an electrical device. In the discharge differential capacitance curve of the positive electrode active material of this application, the ratio of the dQ / dV values ​​of the peak P1 between 3.5 and 3.6V and the peak P2 between 3.6 and 3.9V meets a certain range. This allows the positive electrode active material to have lower impedance while maintaining higher capacity, reduces heat generation during fast charging, improves battery safety performance, and the lower impedance can also slow down battery capacity decay and improve battery cycle life.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] With the rise in electric vehicle sales, charging anxiety and low-temperature range issues are escalating, making the development of cathode materials with low impedance a significant economic benefit. Ternary layered oxide LiNi x Co y Mn z O2 (x+y+z=1) has advantages such as high specific capacity, long cycle life, and good low-temperature performance. In recent years, it has been extensively studied and applied in electric vehicles, plug-in hybrid electric vehicles, and hybrid electric vehicles.

[0003] However, lithium-ion batteries generate significant heat during fast charging, necessitating further reductions in internal resistance to alleviate this heat generation issue. Furthermore, lower internal resistance also allows for improved low-temperature capacity. Summary of the Invention

[0004] Therefore, this application provides a positive electrode active material, a lithium-ion secondary battery, and an electrical device, with the aim of reducing the internal resistance of the positive electrode active material, thereby improving the safety performance and cycle performance of the battery.

[0005] To achieve the above objectives, according to one aspect of this application, a positive electrode active material is provided, the positive electrode active material comprising lithium nickel cobalt oxide, wherein the molar amount of metal elements other than lithium in the lithium nickel cobalt oxide is 1, and the molar content of nickel element is greater than or equal to 0.5. When a coin cell half-cell composed of the positive electrode active material is charged and discharged under the following conditions (1), the discharge differential capacitance curve, with voltage V on the horizontal axis and dQ / dV value differentiated from battery capacity Q on the vertical axis, satisfies the following:

[0006] 0 <P1 / P2≤3;

[0007] Wherein, P1 is the dQ / dV value of peak P1 between 3.5 and 3.6 V; P2 is the dQ / dV value of peak P2 between 3.6 and 3.9 V;

[0008] Condition (1): The critical voltage for charging and discharging is 2.8 to 4.4V; the current density for charging and discharging is 10mA / g.

[0009] Furthermore, peak P1 is the peak with the highest dQ / dV value in the discharge differential capacitance curve; peak P2 is the peak with the largest integrated area in the discharge differential capacitance curve.

[0010] Furthermore, the Dv50 of the positive electrode active material is 2–6.5 μm, and the Dv99 is 8–15 μm.

[0011] Furthermore, the specific surface area of ​​the positive electrode active material is 0.2–1.2 m². 2 / g.

[0012] Furthermore, the residual lithium content on the surface of the positive electrode active material is 500–4800 ppm.

[0013] Furthermore, the compacted density of the positive electrode active material powder is 3.3–3.7 g / cm³. 3 .

[0014] Furthermore, the lithium nickel cobalt oxide includes those with the general formula Li x Ni a Co b R c Me d O e Z f The compound, wherein 0.9≤x≤1.1, a+b+c+d=1, 0.5≤a≤0.77, 0.02≤b≤0.15, 0≤d≤0.12, 1.9≤e≤2, 0≤f≤0.1; R is Mn and / or Al, Me includes at least one of Ti, Zr, Sr, B, Mg, Sn, W, Y, Ta, Si, La, Er, Nd, Gd, Ce, Ba, Nb, Mo, Cr, V, Ca; Z includes at least one of P, S, N, F, Cl, Br, I.

[0015] Furthermore, at least a portion of the surface of the positive electrode active material is provided with a coating layer, the coating layer comprising a coating element, the coating element comprising at least one of Al, Ti, Zr, Ba, Zn, P, and W.

[0016] According to another aspect of this application, a secondary battery is provided, comprising a casing and a cell assembly housed within the casing, the cell assembly comprising a positive electrode plate, the positive electrode plate comprising a current collector and a positive active material layer located on at least one side of the current collector, the positive active material layer comprising the aforementioned positive active material; the secondary battery, during a 4C rate charging process at a temperature of 25±5℃, has a maximum temperature rise ΔT of the casing ≤ 50℃, wherein the cutoff voltage of the charging process is 4.4V.

[0017] According to another aspect of this application, an electrical device is provided, including the aforementioned secondary battery, wherein the secondary battery serves as the power supply for the electrical device.

[0018] In the discharge differential capacitance curve of the positive electrode active material of this application, the dQ / dV ratio of the peak P1 between 3.5 and 3.6V and the peak P2 between 3.6 and 3.9V meets a certain range. This allows the positive electrode active material to have lower impedance while maintaining higher capacity, which can reduce heat generation during fast charging, improve battery safety performance, and slow down battery capacity decay, thus improving battery cycle life. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below.

[0020] Figure 1 This is the discharge differential capacitance curve obtained in Example 1, with voltage V on the horizontal axis and dQ / dV on the vertical axis. Detailed Implementation

[0021] The following will clearly and completely describe the concept and technical effects of this application in conjunction with embodiments, so as to fully understand the purpose, features and effects of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are all within the scope of protection of this application.

[0022] The embodiments of this application are described in detail below. The described embodiments are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0023] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0024] In the description of this application, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0025] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0026] In a typical embodiment of this application, a positive electrode active material is provided, the positive electrode active material comprising lithium nickel cobalt oxide, wherein the molar amount of metal elements other than lithium in the lithium nickel cobalt oxide is 1, and the molar content of nickel element is greater than or equal to 0.5. When the coin cell composed of the positive electrode active material is charged and discharged under the following conditions (1), the discharge differential capacitance curve, with voltage V on the horizontal axis and dQ / dV value differentiated from battery capacity Q by voltage V on the vertical axis, satisfies the following:

[0027] 0 <P1 / P2≤3;

[0028] Wherein, P1 is the dQ / dV value of peak P1 between 3.5 and 3.6 V; P2 is the dQ / dV value of peak P2 between 3.6 and 3.9 V;

[0029] Condition (1): The critical voltage for charging and discharging is 2.8 to 4.4V, and the current density for charging and discharging is 10mA / g.

[0030] In the discharge differential capacitance curve of the positive electrode active material of this application, when the ratio of the dQ / dV values ​​of the peak P1 between 3.5 and 3.6 V and the peak P2 between 3.6 and 3.9 V meets a certain range, it indicates that there is a high content of the three-dimensional phase LT-LICoO2 in the positive electrode active material. Since the phase LT-LICoO2 has excellent kinetic properties, it can make the positive electrode active material have lower impedance while maintaining high capacity, reduce heat generation during fast charging, improve battery safety performance, and the lower impedance can also slow down battery capacity decay and improve battery cycle life.

[0031] In some preferred embodiments, peak P1 is the peak with the highest dQ / dV value in the discharge differential capacitance curve; peak P2 is the peak with the largest integrated area in the discharge differential capacitance curve. In the discharge differential capacitance curve of the positive electrode active material of this application, the ratio of the dQ / dV values ​​of peak P1 between 3.5 and 3.6V and peak P2 between 3.6 and 3.9V meets a certain range, which can enable the positive electrode active material to have lower impedance while maintaining higher capacity, reduce heat generation during fast charging, improve battery safety performance, and slow down battery capacity decay and improve battery cycle life.

[0032] In some preferred embodiments, the particle size Dv50 of the positive electrode active material is 2–6.5 μm, and the particle size Dv99 is 8–15 μm. For example, Dv50 can be 2 μm, 3.5 μm, 5 μm, or 6.5 μm, and Dv99 can be 8 μm, 10 μm, 12 μm, or 15 μm. Having particle sizes Dv50 and Dv99 within these ranges is beneficial for improving electrode compaction and also facilitates ion insertion / extraction within the material at high current densities, thereby improving the battery's capacity and rate performance.

[0033] In some preferred embodiments, the compacted density of the positive electrode active material powder is 3.3–3.7 g / cm³. 3 For example, it can be 3.3 g / cm³. 3 3.4g / cm 3 3.5g / cm 3 3.7g / cm 3 By controlling the compaction density of the positive electrode active material within this range, it is possible to better reduce the internal resistance of the positive electrode active material while increasing its capacity.

[0034] In some preferred embodiments, the specific surface area of ​​the positive electrode active material is 0.2–1.2 m². 2 / g. For example, the specific surface area can be 0.2m². 2 / g, 0.6m 2 / g, 0.8m 2 / g, 1.2m 2 The specific surface area range of / g is one or both of the values. Positive electrode active materials within the above specific surface area range can further reduce CEI film formation, have a moderate contact area with the electrolyte, fewer side reactions during cycling, excellent cycling performance, and are also more favorable for processing and preparation.

[0035] In some preferred embodiments, the residual lithium content on the surface is 500–4800 ppm, for example, it can be one or any two of 500 ppm, 2000 ppm, 3500 ppm, and 4800 ppm. Positive electrode active materials within the above residual lithium content range can further reduce the degree of side reactions with the electrolyte, have a moderate contact area with the electrolyte, fewer side reactions during cycling, excellent cycling performance, and are also more conducive to processing and preparation.

[0036] In some preferred embodiments, the lithium nickel cobalt oxide comprises lithium with the general formula Li x Ni a Co b R c Me d O e Z fThe compound, wherein 0.9≤x≤1.1, a+b+c+d=1, 0.5≤a≤0.77, 0.02≤b≤0.15, 0≤d≤0.12, 1.9≤e≤2, 0≤f≤0.1; R is Mn and / or Al, Me includes at least one of Ti, Zr, Sr, B, Mg, Sn, W, Y, Ta, Si, La, Er, Nd, Gd, Ce, Ba, Nb, Mo, Cr, V, Ca; Z includes at least one of P, S, N, F, Cl, Br, I.

[0037] In this embodiment, the positive electrode active material contains the element Me, which includes at least one of Ti, Zr, Sr, B, Mg, Sn, W, Y, Ta, Si, La, Er, Nd, Gd, Ce, Ba, Nb, Mo, Cr, V, and Ca. Me can be used as a dopant element. These dopant elements not only improve the electrochemical performance and structural stability of the positive electrode material but also act as a flux, enabling low-temperature, high-crystallinity sintering of the material.

[0038] In this embodiment, the positive electrode active material contains element Z, which includes at least one of P, S, N, F, Cl, Br, and I. Element Z can also be used as a dopant element along with element Me, which can reduce surface oxygen activity and improve cycle performance.

[0039] In some preferred embodiments, at least a portion of the surface of the positive electrode active material is provided with a coating layer, the coating layer comprising a coating element, wherein the coating element includes at least one selected from Al, Ti, Zr, Ba, Zn, P, and W. The coating layer can reduce the dissolution of transition elements and also inhibit the corrosion of the positive electrode active material by the electrolyte, thereby improving battery cycle performance.

[0040] In some preferred embodiments, the method for preparing the positive electrode active material includes the following steps:

[0041] Preparation of nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursors;

[0042] The positive electrode active material is obtained by mixing a nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursor with a lithium source, followed by calcination, crushing, and sieving. The nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursor refers to hydroxides containing nickel, cobalt, and manganese (or aluminum) elements.

[0043] In some embodiments of this application, nickel cobalt manganese and / or nickel cobalt aluminum precursors are directly mixed with a lithium source and calcined once. In other embodiments, the nickel cobalt manganese and / or nickel cobalt aluminum precursors may be pretreated to obtain nickel cobalt manganese and / or nickel cobalt aluminum oxides before being mixed with a lithium source and calcined once.

[0044] In some embodiments of this application, the preparation method of nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursors can be a co-precipitation method, in which soluble salts of nickel, cobalt, and manganese (or aluminum) are mixed with a precipitant and a complexing agent to obtain nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursors. The soluble salts of nickel, cobalt, and manganese (or aluminum) include, but are not limited to, at least one of the halide, sulfate, and nitrate salts of nickel-cobalt-manganese and / or nickel-cobalt-aluminum; the precipitant includes, but is not limited to, at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and ammonium carbonate; and the complexing agent includes, but is not limited to, at least one of ammonia, ethylenediaminetetraacetic acid, and tartaric acid. The raw materials can be formulated according to the proportions of the elements in the positive electrode active material.

[0045] In some embodiments of this application, the pH of the reaction system is controlled between 10 and 12, for example, it can be 10, 10.5, 11, 11.5, 12, or further controlled between 11 and 12, or between 11.2 and 11.8.

[0046] In some embodiments of this application, the concentration of the complexing agent is 1 to 15 mol / L, and further 1 to 10 mol / L or 2 to 5 mol / L.

[0047] In some embodiments of this application, the reaction temperature is 40–80°C, and more specifically 40–60°C or 45–55°C.

[0048] In some embodiments of this application, the prepared nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursors are subjected to a first heat treatment to remove free moisture from the surface of the precursors, thereby obtaining a preliminary heat-treated product. Further, the first heat treatment temperature can be 50–100°C, 60–100°C, 70–100°C, 80–100°C, or 90–100°C.

[0049] In some embodiments of this application, the preliminary heat-treated product undergoes a secondary heat treatment to remove hydroxide ions, yielding nickel-cobalt-manganese and / or nickel-cobalt-aluminum hydroxides. Further, the temperature of the secondary heat treatment can be 400–600°C, 500–600°C, or 500–550°C. In some embodiments, after the secondary heat treatment, the nickel-cobalt-manganese and / or nickel-cobalt-aluminum oxides are further washed and dried.

[0050] In some embodiments of this application, after the nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursors are mixed with the lithium source, the temperature of the first calcination is 700-980°C.

[0051] The lithium source includes, but is not limited to, at least one of lithium oxide, lithium phosphate, lithium acetate, lithium hydroxide, lithium carbonate, and lithium nitrate. In some embodiments, since the positive electrode active material is also doped with other metal or non-metal elements, other metal or non-metal element sources can be added during the single calcination process of mixing the nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursor with the lithium source. For example, the nickel-cobalt-manganese and / or nickel-cobalt-aluminum precursor is mixed with the lithium source, a Me source (if present), and a Z source (if present) and then calcined. The Me source and Z source include, but are not limited to, at least one of oxides, hydroxides, Me salts (such as halide salts, carbonates, nitrates, oxalates, etc. of Me), Me salts, Z salts (such as potassium salts, lithium salts, ammonium salts of Z), and Z salts.

[0052] In some embodiments of this application, the temperature of the first calcination is 800–950°C.

[0053] In some embodiments of this application, after the first calcination, the product is further crushed and sieved to obtain a first-calcined product. The first-calcined product can have a suitable particle size and particle size distribution, so it can be used directly as a positive electrode active material. Alternatively, it can be mixed again and calcined a second time to further coat other metal or non-metal elements. After the second calcination, it can also be mixed again and calcined a third time to further coat other metal or non-metal elements.

[0054] In some embodiments of this application, the temperature of the secondary calcination is 500–850°C, and more specifically 600–750°C.

[0055] In some embodiments of this application, the temperature for the three calcinations is 400–550°C, and further, 400–500°C.

[0056] It should be noted that in the above preparation method, for positive electrode active materials with different elemental compositions and ratios, the morphology, particle size and distribution of the active material particles can be controlled by controlling the temperature and time of the first calcination, the specific crushing and screening process and parameters after calcination (e.g., using closed-loop airflow crushing, semi-closed-loop airflow crushing and other airflow crushing processes, adjusting the air intake rate, feed rate, etc.; controlling the sieve size and screening times), as well as possible secondary calcination and time, etc., thereby adjusting its compaction density and conductivity, thus meeting the requirements of this invention.

[0057] The method for preparing the positive electrode active material provided in this application is simple, easy to implement, and cost-effective, and can be applied on a large scale in industrial production.

[0058] A second aspect of this application provides a secondary battery, which may be a lithium-ion secondary battery, comprising a housing and a cell assembly housed within the housing, the cell assembly comprising a positive electrode plate, the positive electrode plate comprising a current collector and a positive active material layer located on at least one side of the current collector, the positive active material layer comprising the aforementioned positive active material.

[0059] In some embodiments, the positive electrode active material layer further includes at least one of a conductive agent and a binder. The conductive agent includes, but is not limited to, at least one of graphite, acetylene black, carbon black, carbon nanotubes, and carbon fibers. The binder includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyurethane (PU), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB). The current collector includes, but is not limited to, at least one of a metal foil (such as aluminum foil, silver foil, tin foil, iron foil, titanium foil, nickel foil, copper foil, or alloy foil of the above metals) and a metal mesh (such as at least one of aluminum mesh, silver mesh, tin mesh, iron mesh, titanium mesh, nickel mesh, copper mesh, or alloy mesh of the above metals).

[0060] In some embodiments of this application, the positive electrode active material layer comprises 70–99 wt% positive electrode active material, 0.5–6 wt% conductive agent, and 0.5–20 wt% binder. Further, the mass fraction of the positive electrode active material in the positive electrode active material layer is 80–99 wt%, 90–99 wt%, or 95–99 wt%; the mass fraction of the conductive agent in the positive electrode active material layer is 1–6 wt% or 2–5 wt%; and the mass fraction of the binder in the positive electrode active material layer is 1–10 wt% or 1–5 wt%.

[0061] In some embodiments of this application, when the positive electrode active material, conductive agent and binder are made into a positive electrode active material layer, the positive electrode active material layer is obtained by dispersing it in a solvent and then coating it in a positive electrode current collector and drying it. For example, N-methylpyrrolidone (NMP) can be used as a solvent.

[0062] In some embodiments of this application, the cell assembly further includes a negative electrode and a separator located between the positive electrode and the negative electrode. After the cell assembly is housed in a housing, an electrolyte is injected, and then it is encapsulated to obtain a secondary battery.

[0063] In some embodiments of this application, the negative electrode sheet includes, but is not limited to, a lithium sheet, a negative electrode current collector with a negative electrode active material layer loaded on its surface, etc. Similar to the positive electrode active material layer, the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0064] In some embodiments of this application, the negative electrode active material includes, but is not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, LiSn alloys, and LiSn. At least one of the following: O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate. The conductive agent, binder, and negative electrode current collector can be selected from at least one of the same range as the conductive agent and binder in the positive electrode. Similarly to the positive electrode, the negative electrode can be prepared by mixing the above-mentioned negative electrode active material, binder, and conductive agent, coating it onto the current collector, drying it, and then further processing it through rolling, cutting, and other steps.

[0065] In some embodiments of this application, the electrolyte may be at least one of liquid electrolyte, gel electrolyte, and solid electrolyte.

[0066] In some embodiments of this application, the diaphragm includes, but is not limited to, a single-layer or multi-layer film of one or more materials selected from polyethylene (PE) and polypropylene (PP).

[0067] In some embodiments of this application, the positive electrode, the negative electrode, and the separator are obtained by at least one of winding, stacking, or other methods to form a cell assembly. The cell assembly is housed in a housing, which can be a soft housing or a hard housing. After injecting electrolyte, the assembly is sealed to obtain a lithium-ion secondary battery.

[0068] It is understood that conductive agents, binders, electrolytes, and diaphragms may also be made from other materials well known in the art or by other methods.

[0069] In some embodiments of this application, the lithium-ion secondary battery casing can be an aluminum-plastic film.

[0070] In some embodiments of this application, the lithium-ion secondary battery casing can be a hard casing or a soft casing.

[0071] In some embodiments of this application, during a 4C charging process at a temperature of 25±5℃, the maximum temperature rise of the casing ΔT≤50℃, wherein the cutoff voltage of the charging process is 4.4V.

[0072] In some embodiments of this application, when the casing is a hard casing, the maximum temperature rise ΔT at the center of the bottom of the hard casing battery is ≤50°C.

[0073] The bottom of the hard-shell battery is positioned opposite the top cover of the battery.

[0074] In some embodiments of this application, when the casing is a soft casing, the maximum temperature rise ΔT at the center of the large surface of the soft casing battery is ≤50℃. Here, the maximum temperature rise refers to the difference between the highest temperature reached by the battery casing and its initial temperature during high-rate charging.

[0075] A third aspect of this application provides an electrical appliance that includes the aforementioned secondary battery.

[0076] Electrical equipment refers to any device that can utilize electrical energy and convert it into mechanical energy, heat energy, light energy, or one or more other forms of energy, such as electric motors, electric heaters, and electric light sources. Specifically, it can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, and energy storage systems. Mobile devices can include mobile phones, laptops, drones, robot vacuum cleaners, and e-cigarettes; electric vehicles can include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and electric trucks.

[0077] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application.

[0078] Example 1

[0079] This embodiment provides a positive electrode active material, comprising matrix particles and a coating layer. The matrix particles are lithium nickel cobalt manganese oxide with the molecular formula Li(Ni) 0.6 Co 0.1 Mn 0.3 ) 0.995 Sr 0.001 Zr 0.003 W 0.001 O2, the coating material is alumina Al2O3 and titanium dioxide TiO2, and based on the weight of the positive electrode active material, the Al element content is 500ppm and the Ti element content is 1000ppm.

[0080] The preparation method of the positive electrode active material is as follows:

[0081] (1) Nickel sulfate, cobalt sulfate, and manganese sulfate were added to deionized water to prepare a nickel-cobalt-manganese sulfate solution, wherein the molar ratio of nickel, cobalt, and manganese in the nickel-cobalt-manganese sulfate solution was Ni:Co:Mn = 61.2:8.2:30.6. A 2 mol / L ammonia solution and an 8 mol / L sodium hydroxide solution were introduced into the solution in a uniform, parallel flow. The ammonia solution contained 0.6% tetraethylammonium hydroxide by mass, and the pH was controlled between 11.2 and 11.8 by sodium hydroxide. Nitrogen gas was used for protection during the reaction, the stirring speed was 500 rpm, and the reaction apparatus temperature was maintained at approximately 50°C. The reaction time was controlled to obtain the ternary precursor Ni. 0.612 Co 0.082 Mn 0.306(OH)2. The ternary precursor was placed in a hot air circulating drying oven and heat-treated at 95°C for 2 hours to obtain a pre-heat-treated product. Then, it was transferred to a calcining furnace and heat-treated at 510°C for 5 hours to obtain a high-temperature product. After washing and drying, the ternary precursor oxide was obtained.

[0082] (2) The ternary precursor oxide, lithium carbonate, and dopants strontium carbonate (SrCO3), zirconium oxide (ZrO2), and tungsten oxide (WO3) were weighed according to the elemental molar ratio of Li:main element (Ni+Co+Mn):Sr:Zr:W = 1:0.995:0.001:0.003:0.001 and added to a mixer for mixing. The mixed material was placed in a tube furnace and calcined for 12 hours at a programmed temperature of 5℃ / min to 935℃ under an oxygen atmosphere. After cooling to room temperature in the furnace, the precursor of active material particles with an average particle size Dv50 of 3.8μm was obtained by airflow crushing and classification.

[0083] (3) The precursor of the active material particles was coated with Co(OH)2 and then calcined again in a furnace at 750℃ for 12 hours to obtain lithium nickel cobalt manganese oxide with the molecular formula Li(Ni 0.6 Co 0.1 Mn 0.3 ) 0.995 Sr 0.001 Zr 0.003 W 0.001 O2.

[0084] (4) The precursor of the active material particles after secondary calcination was coated with alumina Al2O3 and titanium dioxide TiO2 and then calcined three times in a furnace at a temperature of 450℃ for 10 hours. After sieving, the positive electrode active material was obtained.

[0085] This embodiment also provides a lithium-ion secondary battery, the preparation method of which is as follows:

[0086] (1) Preparation of positive electrode sheet

[0087] The prepared positive electrode active material, conductive carbon black SP, and binder PVDF were dispersed in solvent NMP at a mass ratio of 96:3:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on one side of the positive electrode current collector aluminum foil, and after baking, cold pressing, and cutting, a positive electrode sheet was obtained.

[0088] (2) Preparation of negative electrode sheet

[0089] Artificial graphite, conductive carbon black (SP), and binder (PVDF) were dispersed in deionized water at a mass ratio of 95.7:1:3.3 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto one side of the negative electrode current collector copper foil, and after baking, cold pressing, and cutting, a negative electrode sheet was obtained.

[0090] (3) Preparation of electrolyte

[0091] Ethylene carbonate (EC), dimethyl carbonate (DMC), and propylene carbonate (PC) were mixed evenly in a mass ratio of 40:30:30 to obtain an organic solvent. LiPF6 was dissolved in the above organic solvent and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage content of LiPF6 was 12.5%.

[0092] (4) Battery manufacturing

[0093] The positive electrode sheet, PP / PE / PP composite separator and negative electrode sheet are stacked and wound in sequence to obtain the cell assembly. The cell assembly is placed in an aluminum shell for welding and baking. After adding the electrolyte, it is sealed to complete the battery preparation.

[0094] Examples 2-3

[0095] The preparation process is the same as in Example 1. The difference is that the proportions of nickel sulfate, cobalt sulfate and manganese sulfate added in step (1) of the preparation process of the positive electrode active material are adjusted to prepare positive electrode active materials with different proportions of Ni, Co and Mn.

[0096] Examples 4-6

[0097] The preparation process is the same as in Example 1. The difference is that the type and ratio of dopant sources in step (2) of the positive electrode active material preparation process are adjusted to prepare positive electrode active materials with different doping elements.

[0098] Examples 7-10

[0099] The preparation process is the same as in Example 1. The difference is that the type of coating source in step (4) of the positive electrode active material preparation process is adjusted to prepare positive electrode active materials with different coating elements. In Example 10, the coating step is not performed.

[0100] Examples 11-14

[0101] The preparation process is the same as in Example 1. The difference is that the calcination temperature and time in step (2) of the positive electrode active material preparation process are adjusted to obtain positive electrode active materials with different particle size distribution and specific surface area.

[0102] Examples 15-18

[0103] The preparation process is the same as in Example 1. The difference is that the calcination temperature and time in step (3) of the positive electrode active material preparation process are adjusted to obtain positive electrode active materials with different P1 / P2 ratios.

[0104] Comparative Example 1

[0105] The preparation process is the same as in Example 1. The difference is that in step (3) of the preparation process of the positive electrode active material, Co(OH)2 is not added, and a positive electrode active material with P1 / P2 of 0 is obtained.

[0106] Comparative Example 2

[0107] The preparation process is the same as in Example 1. The difference is that the calcination temperature and time in step (3) of the positive electrode active material preparation process are adjusted to obtain a positive electrode active material with P1 / P2 of 3.2.

[0108] The testing methods for relevant characteristics and performance are as follows:

[0109] 1. Determination of P1 / P2 ratio in lithium-ion secondary batteries

[0110] The lithium-ion secondary batteries prepared in each embodiment and comparative example were subjected to charge and discharge cycle tests at a current density of 10 mA g. -1 3 charge / discharge cycles, 10mA g -1 Three charge-discharge cycles were performed, and the voltage V and battery capacity Q were measured on the sixth cycle. The discharge differential capacitance curve was calculated with the voltage V as the horizontal axis and the dQ / dV value (the derivative of voltage V with respect to battery capacity Q) as the vertical axis. Peak P1 is the peak with the highest dQ / dV value in the discharge differential capacitance curve; peak P2 is the peak with the largest integrated area in the discharge differential capacitance curve. The ratio of dQ / dV values ​​of peaks P1 and P2 is shown in Table 1. The critical voltage for charging and discharging is 2.8-4.4V. (See also...) Figure 1 .

[0111] 2. Surface residual lithium content determination: The test results were obtained in accordance with GB / T 9725-2007.

[0112] 3. Measurement of physical parameters

[0113] (1) Particle size distribution determination: The particle size distribution was determined by laser diffraction method according to GB-T 19077-2016.

[0114] (2) Specific surface area determination: The specific surface area of ​​solid materials was determined by gas adsorption BET method according to GB / T 19587-2017.

[0115] (3) Compacted density determination: The density was obtained by referring to GB / T 24533-2019.

[0116] 4. DC Impedance (DCR) Measurement

[0117] At 25℃, the battery was charged at a constant current rate of 0.33C to 4.35V, and then charged at a constant voltage rate until the current was less than or equal to 0.05C. After that, the soft pack battery was discharged at a constant current rate of 0.33C to adjust the state of charge (SOC) to 90%, 50%, and 20%, respectively. Then, it was discharged at 5C for 10s at SOC of 90%, 50%, and 20%, respectively. The voltage drop before and after discharge was recorded. The ratio of the voltage drop before and after discharge to the discharge current is the DC resistance DCR of the battery. The DC resistance DCRs at 90%, 50%, and 20% were obtained, as shown in Table 2.

[0118] 5. Determination of the maximum temperature rise ΔT of the casing during 4C charging: In an environment with a temperature of 25±5℃, temperature sensors were placed at the battery tabs and the center of the casing, respectively. The battery was left to stand for 30 minutes until the temperature stabilized, and then charged at a 4C rate to 100% SOC (voltage of 4.4V). The temperature change of the sensors was recorded to obtain the maximum temperature rise of the battery during the charging process, as shown in Table 2.

[0119] 6. Determination of gram capacity: using 10 mA g -1 The battery was charged to its upper limit voltage of 4.4V at a current density, left to stand for 5 minutes, and then charged at a current density of 10mA g. -1 The current discharged the battery to the lower limit voltage of 2.8V, and the specific capacity was calculated, as shown in Table 2.

[0120] 7. Cyclic performance testing

[0121] Determination of capacity retention: using 200 mAg -1 The current charges the battery to its upper limit cutoff voltage of 4.4V, then maintains a constant voltage of 4.4V until the current reaches 5mA. -1 Then at 200mA g -1 The current discharges the battery to the lower cutoff voltage of 2.8V, and this cycle is repeated 1200 times. The capacity retention rate after 1200 cycles is then calculated.

[0122] Table 1

[0123]

[0124]

[0125] Table 2

[0126]

[0127]

[0128] According to the above data, when in the discharge differential capacitance curve of the positive electrode active material, the ratio of the dQ / dV values of peak P1 between 3.5 and 3.6 V and peak P2 between 3.6 and 3.9 V satisfies: 0 < P1 / P2 ≤ 3, the battery has a high energy density and excellent cycle performance. At the same time, the maximum temperature rise of the battery is also low, and the overall performance of the battery is excellent.

[0129] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material contains lithium nickel cobalt oxide. Taking the molar amount of metal elements other than lithium in the lithium nickel cobalt oxide as 1, the molar content of nickel element is greater than or equal to 0.

5. When the coin cell composed of the positive electrode active material is charged and discharged under the following conditions (1), the discharge differential capacitance curve, with voltage V on the horizontal axis and dQ / dV value differentiated from battery capacity Q on the vertical axis, satisfies the following: 1.7≤P1 / P2≤3; Wherein, P1 is the dQ / dV value of peak P1 between 3.5 and 3.6 V; P2 is the dQ / dV value of peak P2 between 3.6 and 3.9 V; Condition (1): The critical voltage for charging and discharging is 2.8~4.4V, with a current density of 10 mA g. -1 3 charge / discharge cycles, 10mA g -1 The battery was charged and discharged for 3 cycles, and the voltage V and battery capacity Q were measured on the 6th cycle.

2. The positive electrode active material according to claim 1, characterized in that, Peak P1 is the peak with the highest dQ / dV value in the discharge differential capacitance curve; peak P2 is the peak with the largest integrated area in the discharge differential capacitance curve.

3. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material has a Dv50 of 2~6.5μm and a Dv99 of 8~15μm.

4. The positive electrode active material according to claim 1, characterized in that, The compacted density of the positive electrode active material powder is 3.3~3.7 g / cm³. 3 .

5. The positive electrode active material according to claim 1, characterized in that, The specific surface area of ​​the positive electrode active material is 0.2~1.2 m². 2 / g.

6. The positive electrode active material according to claim 1, characterized in that, The residual lithium content on the surface of the positive electrode active material is 500–4800 ppm.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that, The lithium nickel cobalt oxide includes those with the general formula Li x Ni a Co b R c Me d O e Z f The compound, wherein 0.9≤x≤1.1, a+b+c+d=1, 0.5≤a≤0.77, 0.02≤b≤0.15, 0≤d≤0.12, 1.9≤e≤2, 0≤f≤0.1; R is Mn and / or Al, Me includes at least one of Ti, Zr, Sr, B, Mg, Sn, W, Y, Ta, Si, La, Er, Nd, Gd, Ce, Ba, Nb, Mo, Cr, V, Ca; Z includes at least one of P, S, N, F, Cl, Br, I.

8. The positive electrode active material according to claim 1, characterized in that, At least a portion of the surface of the positive electrode active material is provided with a coating layer, the coating layer comprising a coating element, the coating element comprising at least one of Al, Ti, Zr, Ba, Zn, P, and W.

9. A secondary battery, characterized in that, The battery includes a housing and a cell assembly housed within the housing. The cell assembly includes a positive electrode plate, the positive electrode plate including a current collector and a positive active material layer located on at least one side of the current collector, the positive active material layer including the positive active material according to any one of claims 1 to 8; during a 4C rate charging process at a temperature of 25±5℃, the maximum temperature rise ΔT of the housing is ≤50℃, wherein the cutoff voltage of the charging process is 4.4V.

10. An electrical appliance, characterized in that, The device includes the secondary battery as described in claim 9, wherein the secondary battery serves as the power supply for the electrical equipment.

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