Positive electrode active material, positive electrode sheet, and lithium-ion battery

Abstract

A positive electrode active material, a positive electrode sheet, and a lithium-ion battery. The positive electrode active material comprises a matrix and a coating layer covering at least part of the surface of the matrix. The matrix comprises a lithium metal oxide, and the lithium metal oxide is a Cmca space group of a cubic crystal system and has a 002 peak with a 2θ of 17.9° to 18.1° and a 131 peak with a 2θ of 67.0° to 67.5°. The coating layer comprises selenium. The positive electrode active material is conducive to improving the specific capacity and cycle performance of a battery.

Description

Positive electrode active material, positive electrode sheet and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 14, 2023, with application number 202310709284.0 and application name “A positive electrode active material, positive electrode sheet and lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to a pole piece material, and in particular to a positive electrode active material, a positive electrode piece and a lithium-ion battery, belonging to the technical field of secondary batteries. Background Art

[0003] With the development and progress of lithium-ion battery technology, higher and higher requirements are placed on its capacity. In the composition of lithium-ion batteries, the capacity of the positive electrode active material plays a vital role in the capacity of lithium-ion batteries.

[0004] To increase the capacity of lithium-ion batteries, the most common method currently is to increase their charge and discharge voltage. However, as the voltage increases, the crystal structure of the positive electrode active material collapses, leading to a series of problems such as rapid capacity decay and a significant decrease in cycle performance.

[0005] Therefore, developing a lithium-ion battery positive electrode active material with high specific capacity and excellent cycle performance is a technical problem that needs to be solved urgently in this field.

[0006] Summary of the Invention

[0007] The present application provides a positive electrode active material. By coating the surface of the positive electrode active material with Se elements, after the positive electrode active material is applied to a lithium ion battery, the lithium ion battery can have both excellent specific capacity and cycle stability, and is particularly suitable for high-voltage environments.

[0008] The present application provides a positive electrode sheet, which includes the above-mentioned positive electrode active material, thereby helping to improve the gram capacity and cycle performance of the battery.

[0009] The present application also provides a lithium-ion battery, which includes the above-mentioned positive electrode active material or positive electrode sheet, so that the lithium-ion battery has excellent performance in terms of gram capacity and cycle performance.

[0010] The present application provides a positive electrode active material, comprising a substrate and a coating layer covering at least a portion of the surface of the substrate;

[0011] Wherein, the matrix comprises lithium metal oxide represented by Formula 1 and / or Formula 2, and the coating layer comprises selenium; Li n1-y1 Nay1 Co e1 M1 b1 M2 a1 O2 Formula 1 Li n2-y2-b2 Na y2 Co e2 M1 b2 M2 a2 O2 Formula 2

[0012] In Formula 1, 0.6 ≤ n1 ≤ 1.0, 0 < y1 ≤ 0.05, 0.8 ≤ e1 ≤ 1.03, 0 ≤ a1 ≤ 0.1, 0 < b1 ≤ 0.1, 0 < b1 / (1 - a1 - b1) < 0.1; in Formula 2, 0.6 ≤ n2 ≤ 1.0, 0 < y2 ≤ 0.05, 0.8 ≤ e2 ≤ 1.03, 0 ≤ a2 ≤ 0.1, 0 < b2 ≤ 0.02; in Formula 1 and Formula 2, M1 is selected from at least one of Te, W, Al, B, P, Se, Ti, La, Zr, and K; M2 is a doping element different from M1;

[0013] The lithium metal oxide is of the Cmca space group of the cubic crystal system and has a 002 peak with 2θ of 17.9° - 18.1° and a 131 peak with 2θ of 67.0° - 67.5°.

[0014] The positive electrode active material as described above, wherein the coating layer includes a first coating layer and a second coating layer in the direction away from the substrate; the first coating layer includes at least one of a metal compound and the selenium element, and the second coating layer includes at least one of a metal compound and the selenium element;

[0015] Preferably, the compositions of the first coating layer and the second coating layer are different.

[0016] The positive electrode active material as described above, wherein the first coating layer includes a metal compound and the second coating layer includes a selenium element; or,

[0017] The first coating layer includes a selenium element and the second coating layer includes a metal compound.

[0018] The positive electrode active material as described above, wherein the coating layer containing the selenium element is a selenium single - element layer or a selenium - metal alloy layer.

[0019] The positive electrode active material as described above, wherein the mass percentage content of the selenium element in the positive electrode active material is less than 5000 ppm.

[0020] The positive electrode active material as described above, wherein the metal compound includes at least one of lithium - containing oxide, aluminum - containing oxide, magnesium - containing oxide, zirconium - containing oxide, and titanium - containing oxide.

[0021] The positive electrode active material as described above, wherein the lithium ion conductivity of the lithium-containing oxide is greater than or equal to 1×10 -3 S / cm; and / or,

[0022] The lithium-containing oxide includes at least one of LATP, LLTO, LLZO, Li3BO3, and Li3PO4.

[0023] The positive electrode active material as described above, wherein the thickness of the first coating layer is not greater than 20 nm; and / or the thickness of the second coating layer is not greater than 100 nm.

[0024] The positive electrode active material as described above, wherein the Dv50 of the matrix is ​​12 to 18 μm; and / or M2 includes at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B and P elements.

[0025] The present application provides a positive electrode sheet, which includes any one of the positive electrode active materials described above.

[0026] The positive electrode sheet as described above has a gram capacity of ≥225 mAh / g under the condition that the button battery voltage is ≥4.55V.

[0027] The present application also provides a lithium-ion battery, which includes any of the above-mentioned positive electrode active materials or positive electrode sheets.

[0028] The lithium-ion battery as described above has an operating voltage greater than or equal to 4.5V.

[0029] The lithium-ion battery as described above, wherein the lithium-ion battery further comprises a negative electrode sheet, and the negative electrode sheet comprises a lithium-containing layer.

[0030] The positive electrode active material of the present application has a special crystal phase structure, chemical composition and Se coating structure. After being applied to lithium-ion batteries, the cycle performance and gram capacity of the battery are significantly improved. Even under high-voltage conditions of 4.5V and above, the positive electrode active material will not suffer from structural collapse due to poor pressure resistance. This good structural stability can ensure the deintercalation and extraction of more lithium ions, thereby showing excellent gram capacity and cycle performance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a partial structural diagram of an embodiment of a negative electrode sheet in a lithium-ion battery of the present application;

[0032] FIG2 is a TEM image of the intermediate positive electrode active material 1B in Example 1 of the present application;

[0033] Figure 3 is the TEM image of the positive electrode active material 1C of Example 1 of the present application;

[0034] Figure 4 is the charge-discharge curve of the coin cell assembled with the positive electrode active material of Example 1 of the present application;

[0035] Figure 5 is the XRD pattern of the positive electrode active material of Example 1 of the present application;

[0036] Figure 6 is the XRD pattern of the positive electrode active material of Example 6 of the present application. Detailed Embodiments

[0037] To make the purpose, technical solutions, and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0038] The first aspect of the present application provides a positive electrode active material, which includes a matrix and a coating layer covering at least part of the surface of the matrix;

[0039] Among them, the matrix includes a lithium metal oxide represented by Formula 1 and / or Formula 2, and the coating layer includes selenium element; Li n1-y1 Na y1 Co e1 M1 b1 M2 a1 O2 Formula 1 Li n2-y2-b2 Na y2 Co e2 M1 b2 M2 a2 O2 Formula 2​​​​​​​

[0042] The positive electrode active material of the present application has a core-shell coating structure, wherein the substrate exists as the core and the coating layer coats at least a portion of the surface of the substrate.

[0043] Wherein, the matrix includes the lithium metal oxide represented by Formula 1 and / or Formula 2, that is, the lithium metal oxide may include only the compound represented by Formula 1, may include only the compound represented by Formula 2, or may include both the compounds represented by Formula 1 and Formula 2. Of course, based on the composition of Formula 1 and Formula 2, Formula 1 and Formula 2 may also represent the same compound. In addition, the present application does not limit the specific selection of M2, which may be a common doping element in the art, for example, at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B and P; the coating layer includes selenium.

[0044] It should be noted that n1 in Formula 1 and n2 in Formula 2 are parameters related to the molar amount of elemental lithium in the lithium metal oxide. In detail, when the above-mentioned positive electrode active material has not undergone any charge and discharge treatment, 0.6≤n1≤0.8, 0.6≤n2≤0.8; when the positive electrode active material is applied to a lithium-ion battery for charge and discharge treatment, n1 and n2 will change under different charge and discharge mechanisms and charge and discharge nodes. For example, when a positive electrode sheet including a positive electrode active material and a lithium metal negative electrode sheet are assembled into a battery and charged and discharged, when the remaining charge SOC of the battery is 0 (i.e., in a fully discharged state) and the discharge cut-off voltage is 3.0~3.6V, the values ​​of n1 and n2 of the lithium metal oxide are between 0.7 and 1.0. It should be noted that the change in the values ​​of n1 and n2 refers to the number of charge and discharge cycles within 10. The reason is that the lithium metal oxides represented by Formulas 1 and 2, which have the aforementioned crystal structures, contain some vacancies. Therefore, when they are used for charge and discharge, these vacancies can accept lithium atoms from the lithium negative electrode, thereby increasing the molar amount of lithium ions compared to before charge and discharge. This characteristic helps further improve the battery's cycle performance and specific capacity.

[0045] This application does not limit the detection method of n1 and n2. For example, the positive electrode active material can be detected by an inductively coupled plasma spectrometer (ICP). Alternatively, when detecting the positive electrode active material in the positive electrode sheet, the discharged battery is disassembled and the positive electrode sheet is taken out. The positive electrode sheet is soaked in dimethyl carbonate (DMC) for 1-3 hours or rinsed with DMC, and then naturally dried in a drying room. It is then placed in a muffle furnace and calcined at 300-600°C for 2-5 hours. After that, the active layer falls off the current collector and is sieved with 200 mesh to obtain the powder to be detected. The metal elements in the powder to be detected are then detected by ICP to calculate n1 and n2.

[0046] According to the above-mentioned solution provided in the present application, compared with other positive electrode active materials, after the positive electrode active material including the lithium metal oxide is applied to the lithium ion battery, the specific capacity and cycle performance of the lithium ion battery are significantly improved, and the electrical performance of the lithium ion battery will not deteriorate even under high voltage working conditions.

[0047] Based on the analysis of this phenomenon, the inventors believe that it may be: on the one hand, the present application provides a coating layer containing Se elements, so that the positive electrode active material is a core-shell structure including a lithium metal oxide core and a coating layer covering the core. The coating layer helps to reduce or inhibit the side reactions of lithium metal oxide and the electrolyte. Even when the battery is working under high voltage, a stable interface can still be formed between the positive electrode active material and the electrolyte, and the cycle performance of the battery is improved by avoiding the transition dissolution of metal ions in the positive electrode active ions and avoiding liquid deficiency. At the same time, the inhibition or reduction of side reactions can also reduce the gas production inside the battery, thereby ensuring the safety performance of the battery; on the other hand, the selenium element in the coating layer has good electron transport performance, which makes the positive electrode active material have excellent conductivity, thereby improving the discharge capacity and cycle performance of the lithium-ion battery.

[0048] In addition, the lithium metal oxide with the above-mentioned crystal characteristics has a more complete layered crystal phase structure, which can reduce or inhibit the occurrence of internal mixing of the crystal phase, thereby enabling the smooth deintercalation of lithium ions. Especially during the high-voltage charge and discharge process, it exhibits multiple charge and discharge small platforms with excellent discharge capacity, ensuring discharge and cycle stability under high voltage.

[0049] Specifically, the first-stage discharge capacity of the positive electrode active material accounts for C1 / C0≥9%, and the second-stage discharge capacity accounts for C2 / C0≥25%; wherein C0 is the discharge capacity of a half-cell including the positive electrode active material when subjected to a discharge treatment at a voltage of 3.0 to 4.55V; in the discharge treatment, the capacity of the half-cell when discharged from the initial discharge voltage to 4.4V is defined as C1, and the capacity released when the half-cell is discharged from 3.8V to 3.7V is defined as C2.

[0050] It should be explained that the above discharge capacity is achieved under a special discharge mechanism. Specifically, after the half-cell consisting of a positive electrode sheet of positive electrode active material and a lithium metal negative electrode is charged to an SOC of 100% (the charging mechanism is not specifically limited), it is discharged at 0.1C at 3.0-4.55V. The amount of electricity released when discharging from 4.55V to 4.4V at 0.1C is C1. When discharging from 3.8V to 3.7V, the amount of electricity released in this step-down phase is C2. When discharging further to 3.0V (at which point the SOC is 0), the total amount of electricity released at the beginning of self-discharge is C0.

[0051] It is clear that during the discharge process under high voltage, both the first-stage discharge capacity ratio and the second-stage discharge capacity ratio performed well. Therefore, the positive electrode active material including the lithium metal oxide of the present application has strong pressure resistance, and thus the specific capacity of the battery can be increased by performing a voltage boost process.

[0052] Furthermore, the above-mentioned coating layer of the present application includes a first coating layer and a second coating layer in sequence in the direction away from the substrate, and the first coating layer includes at least one of a metal compound and selenium element, and the second coating layer includes at least one of a metal compound and the selenium element.

[0053] The above-mentioned double-layer coating configuration can not only further reduce or inhibit the side reaction between lithium metal oxide and electrolyte, but also promote the improvement of discharge capacity and discharge stability of the positive electrode active material to a certain extent.

[0054] In detail, the material of the first coating layer and the material of the second coating layer independently include at least one of a metal compound and a selenium element, that is, the two can be the same or different. Especially when the two are different, the degree of improvement in the electrical performance of the lithium-ion battery is more prominent.

[0055] In a specific embodiment, the first coating layer comprises a metal compound, and the second coating layer comprises selenium. That is, the first coating layer and the second coating layer have different compositions, and the material of the first coating layer comprises a metal compound, and the material of the second coating layer comprises selenium.

[0056] In another embodiment, the first coating layer comprises selenium and the second coating layer comprises a metal compound. That is, the first coating layer and the second coating layer have different compositions, and the material of the first coating layer comprises selenium and the material of the second coating layer comprises a metal compound.

[0057] The inventors have found that when the first coating layer includes a metal compound and the second coating layer includes selenium, not only is the operability of preparing the positive electrode active material higher, but the electrical properties of the lithium-ion battery, including cycle performance and specific capacity, are also better.

[0058] Specifically, the aforementioned coating layer comprising the selenium element is a single-substance selenium layer or a selenium-metal alloy layer. In the case of a selenium-metal alloy layer, the present application does not limit the choice of metal alloy, and examples include lithium-selenium alloys, ferroselenium alloys, and selenium-zinc alloys. In practice, due to the lower melting point of single-substance selenium, the use of a single-substance selenium layer as the coating layer comprising the selenium element simplifies the preparation process and saves costs, while also achieving good capacity and cycle performance.

[0059] Furthermore, when the mass percentage of selenium in the positive electrode active material is less than 5000 ppm, it is beneficial to improve the lithium ion intercalation and deintercalation performance of the positive electrode active material, so that the specific capacity and cycle performance of the lithium ion battery are more significantly improved.

[0060] The present application does not limit the specific selection of the metal compound, which may include at least one of lithium-containing oxides, aluminum-containing oxides, magnesium-containing oxides, zirconium-containing oxides, and titanium-containing oxides.

[0061] In specific applications, the specific capacity of the positive electrode active material can be further improved by limiting the lithium ion conductivity of the lithium-containing oxide.

[0062] In a specific embodiment, the lithium ion conductivity of the lithium-containing oxide is at least greater than 1×10 -3 S / cm.

[0063] Exemplarily, the lithium-containing oxide includes at least one of LATP (lithium aluminum titanium phosphate), LLTO (lithium lanthanum titanium oxide), LLZO (lithium lanthanum zirconium oxide), Li 3 BO 3 , and Li 3 PO 4 .

[0064] As previously mentioned, one of the first and second coating layers in the positive electrode active material of this application also includes selenium. Furthermore, when the Dv50 (particle size at which the cumulative volume reaches 50% of the total volume of the positive electrode active material) of the positive electrode active material of this application is 12-18 μm, this facilitates material processing. The inventors speculate that this may be because positive electrode active materials with this particle size exhibit excellent fluidity, making it easier to form a dense packing state.

[0065] Furthermore, the present application does not impose any additional restrictions on the thickness of the first coating layer and the second coating layer. When the thickness of the first coating layer is not greater than 20 nm, and / or the thickness of the second coating layer is not greater than 100 nm, it is beneficial for the intercalation and deintercalation of lithium ions, further increasing the specific capacity of the positive electrode active material.

[0066] For example, the thickness of the first cladding layer may be 2 nm, 5 nm, 7 nm, 10 nm, 13 nm, 15 nm, 18 nm, or 20 nm; the thickness of the second cladding layer may be 10 nm, 15 nm, 27 nm, 40 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0067] The positive electrode active material of the present application may have a single crystal or polycrystalline morphology, with the specific morphology being related to the selection and ratio of the doping elements. Specifically, when the morphology is polycrystalline, the active material is spherical or quasi-spherical; when the morphology is single crystal, the active material may be whisker-like, flake-like, or any other irregular shape.

[0068] The present application does not limit the preparation method of the positive electrode active material. Taking the example that the first coating layer includes a metal compound and the second coating layer includes selenium, for example, the first coating layer is coated on the surface of the lithium metal oxide shown in Formula 1 and / or Formula 2 using atomic layer vapor deposition (ALD) to obtain an intermediate positive electrode active material; then the intermediate positive electrode active material is mixed with the second coating source and sintered to form a second coating layer on the surface of the first coating layer to obtain the positive electrode active material of the present application.

[0069] In a specific embodiment, the lithium metal oxide represented by Formula 1 and / or Formula 2 is placed in the reaction chamber of an ALD reaction device, the reaction temperature is controlled, the first coating source is introduced into the reaction chamber by an inert gas as a carrier gas, and the atomic layer is vapor-deposited on the surface of the lithium metal oxide in an intermittent pulse manner to form a first coating layer (i.e., an intermediate positive electrode active material) including a metal compound on the lithium metal oxide; subsequently, the intermediate positive electrode active material and the second coating source are evenly mixed by a mixing device, and the mixture is passed into a corresponding sintering device for sintering treatment to obtain the positive electrode active material of the present application.

[0070] The above-mentioned first coating source refers to the raw material used to form the first coating layer. For example, when the first coating layer is LATP, the first coating source is a lithium source (for example, lithium tert-butoxide, lithium bis(trimethylsilyl)amide and other organic lithium-containing compounds), an aluminum source (for example, trimethylaluminum and other aluminum-containing organic compounds), a phosphorus source (for example, trimethylphosphine and other phosphorus-containing organic compounds) and a titanium source (for example, titanium tetrachloride and other titanium-containing organic compounds); when the first coating layer is aluminum oxide, the first coating source is, for example, trimethylaluminum and other aluminum-containing organic compounds; when the first coating layer is magnesium oxide, the first coating source is, for example, bis(cyclopentadienyl)magnesium and other magnesium-containing organic compounds.

[0071] During the process of forming the first coating layer, the reaction temperature is 120°C to 350°C, for example, 150°C, 170°C, 180°C, 220°C, 250°C, 270°C, 300°C, 330°C, or 350°C.

[0072] In the process of forming the first cladding layer, the number of interval pulses is 20 to 220 times, for example, 30 times, 50 times, 70 times, 90 times, 100 times, 120 times, 140 times, 150 times, 150 times, or 200 times.

[0073] During the process of forming the first coating layer, the inert gas includes argon or nitrogen. Furthermore, the inert gas is introduced into the reaction chamber as a carrier gas at a flow rate of 20-100 mL / min, for example, 20 mL / min, 40 mL / min, 50 mL / min, 80 mL / min, or 100 mL / min.

[0074] The above-mentioned second coating source refers to the raw material for forming the second coating layer. For example, when the second coating layer is a selenium single-element layer, the second coating source is selenium single-element; when the second coating layer is a selenium-metal alloy layer, the second coating source can be a lithium-selenium alloy, a selenium-iron alloy, a selenium-zinc alloy, etc. During the process of forming the second coating layer, the selenium content in the cathode active material is controlled by controlling the mass of selenium in the second coating source.

[0075] During the above-mentioned process of forming the second coating layer, the temperature of the sintering treatment is 200 - 350 °C, further 250 - 350 °C; the time of the sintering treatment is 5 - 60 min, further 25 - 50 min.

[0076] This application does not limit the preparation method of the lithium metal oxide shown in the above formula 1 and formula 2. In a specific embodiment, the lithium metal oxide of this application can be prepared by mixing the sodium metal oxide shown in formula 1a and 2a with a lithium compound and performing an ion treatment method.

[0077] Na x1 Co e1 M1 b1 M2 a1 O2 Formula 1a Na x2 Co e2 M1 b2 M2 a1 O2 Formula 2a

[0078] In formula 1a, 0.68 < x1 < 0.74, 0.8 ≤ e1 ≤ 1.03, 0 < b1 < 0.1, 0 ≤ a < 0.10, 0 < b1 / (1 - a1) < 0.05; in formula 2a, 0.68 < x2 < 0.74, 0.8 ≤ e2 ≤ 1.03, 0 < b2 < 0.02, 0 ≤ a2 < 0.1.

[0079] The above-mentioned ion exchange treatment is a heat treatment process, specifically referring to mixing the sodium metal oxide and the lithium compound and performing heat treatment at 80 °C - 300 °C for no more than 10 h. After the ion exchange treatment, the ion-exchanged system is washed and dried to finally obtain the lithium metal oxide. Among them, the drying temperature is 80 - 180 °C and the time is at least 10 h. There is no limitation on the equipment for ion exchange treatment and the drying equipment. For example, the equipment for ion exchange treatment can be a closed container equipment with a closed function and stirring ability, such as a wet coating reaction equipment, a co-precipitation reaction equipment, etc.; the drying equipment can be a blast oven, a vacuum drying oven, a rotary kiln, a tray dryer, an oven, etc.

[0080] The lithium compound can be a lithium source compound commonly used in the art, such as at least one of lithium carbonate, lithium chloride, lithium bromide, lithium iodide, lithium nitrate, lithium hydroxide, and lithium fluoride. During the ion exchange treatment, the mass ratio of the lithium compound to the sodium metal oxide is not less than 1:1, preferably (1-3):1.

[0081] Furthermore, when a positive electrode active material having a coating layer covering a lithium metal oxide is to be prepared, a raw material for the coating layer needs to be added in addition to the raw materials including the sodium metal oxide and the lithium compound during the ion exchange process.

[0082] For the sodium metal compounds represented by Formula 1a and Formula 2a, for example, they can be prepared by a method comprising the following steps:

[0083] The cobalt source, the sodium source, the M1 source, and the M2 source are mixed in a target ratio and then calcined to obtain the sodium metal compounds represented by Formula 1a and Formula 2a.

[0084] Specifically, the calcination temperature is 700-900°C for 8-50 hours, and the calcination can be carried out in an oxygen or air atmosphere. The calcination equipment can be, for example, a muffle furnace, a tunnel furnace, a roller kiln, a tubular furnace, or other high-temperature sintering equipment.

[0085] Mixing of the above-mentioned sources can be performed using high-speed mixers, sand mills, ball mills, plowshare mixers, inclined mixers, etc. It should be noted that if a sand mill or ball mill is used and a solvent (water, ethanol, or other solvent medium) is added during the ball or sand milling process, the mixed system must be dried after the mixing process. Generally, the mixing time should not exceed 4 hours.

[0086] This application does not limit the specific selection of cobalt source, sodium source, M1 source and M2 source. For example, the cobalt source is selected from one or more of cobalt hydroxide, cobalt trioxide, doped cobalt trioxide, cobaltous oxide, cobalt oxyhydroxide, cobalt nitrate, cobalt sulfate, etc.; the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, sodium sulfate, etc.; the M1 source can be any compound containing M1, such as an oxide of M1. When M1 is W, the M1 source is, for example, tungstic acid and / or sodium tungstate; when M1 is Te, the M1 source is, for example, telluric acid and / or sodium tellurate; when M1 is Al, the M1 source is, for example, aluminum sulfate. , aluminum nitrate, aluminum hydroxide, etc.; when M1 is B, the M1 source is, for example, boric acid and / or sodium borate, etc.; when M1 is P, the M1 source is, for example, phosphoric acid and / or sodium phosphate, etc.; when M1 is K, the M1 source is, for example, one or more of potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, etc.; the M2 source can be any compound containing M2, such as an oxide of M2, such as one or more of basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthanum oxide, lanthanum fluoride, nickel oxide, niobium oxide, etc.

[0087] A second aspect of the present application provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect.

[0088] Based on the characteristics of the positive electrode active material of the first aspect, the positive electrode sheet of the present application helps to improve the cycle performance and specific capacity of the battery.

[0089] The present application does not limit the specific structure of the positive electrode sheet. For example, the positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active layer provided on at least one surface of the positive electrode current collector, and the positive electrode active layer includes the aforementioned positive electrode active material. It can be understood that in addition to the positive electrode active material, the positive electrode active layer also includes a conductive agent and a binder. Exemplarily, the positive electrode active layer includes 70-99wt% of the positive electrode active material, 0.5-15wt% of the conductive agent, and 0.5-15wt% of the binder in terms of mass percentage. Further, it includes 80-98wt% of the positive electrode active material, 1-10wt% of the conductive agent, and 1-10wt% of the binder.

[0090] The selection of the conductive agent and the binder is not special and can be conventionally selected in the art. For example, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon fiber, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), PVDF-HFP, polytetrafluoroethylene (PTFE), polyacrylate lithium (PAALi), and polypropylene (PAA).

[0091] Furthermore, to enhance safety, a safety layer can be placed between the positive electrode active layer and the current collector. The safety layer can be made of non-conductive safety materials, such as iron-containing compounds (such as lithium iron phosphate and lithium phosphate), aluminum-containing compounds (such as aluminum oxide), silicon oxide, high-resistance carbon black, and PTC materials. Of course, the safety layer also includes a binder, and the ratio of binder to safety material can be further determined based on specific needs.

[0092] Optionally, the safety layer may also be made of a conductive material, such as conductive titanium dioxide.

[0093] A third aspect of the present application provides a lithium-ion battery, which includes the positive electrode active material of the first aspect or the positive electrode sheet of the second aspect, and thus has outstanding performance in terms of cycle performance and specific capacity.

[0094] The present application does not limit the specific structure of the lithium-ion battery, for example, it can be a square shell or a cylindrical battery, etc. In addition to the positive electrode sheet, the lithium-ion battery of the present application also includes a negative electrode sheet, a separator and an electrolyte.

[0095] Exemplarily, the electrolyte is a conventional electrolyte known in the art comprising a lithium salt and a solvent, wherein the solvent contains ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC), propylene carbonate (abbreviated as PC), or fluoroethylene carbonate (abbreviated as FEC).

[0096] Furthermore, the invention also includes an additive represented by formula T, whose mass percentage in the electrolyte is 0.1-10%. The additive is combined with the positive electrode material to meet the battery's working conditions under high voltage (≥4.5V).

[0097] Exemplarily, the negative electrode sheet can be a negative electrode sheet containing a lithium layer, for example, a lithium foil or a negative electrode sheet as shown in FIG1 . Specifically, the negative electrode sheet in FIG1 includes a negative electrode current collector 101, a negative electrode active layer 20 and a lithium material layer 30 that are stacked. The negative electrode sheet in FIG1 is double-sided, and of course, it can also be a negative electrode sheet in which the negative electrode active layer 20 and the lithium material layer 30 are only provided on one side of the negative electrode current collector 101. The lithium material layer is, for example, lithium foil. Furthermore, the surface density of metallic lithium in the lithium material layer is 0.09 mg / cm 2 ~3.5mg / cm 2 ; The negative electrode active layer includes a negative electrode active material, a conductive agent and a binder.

[0098] In one embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of a negative electrode active material, 0.5-15 wt% of a conductive agent, and 0.5-15 wt% of a binder. Furthermore, the negative electrode active layer comprises 80-98 wt% of a negative electrode active material, 1-10 wt% of a conductive agent, and 1-10 wt% of a binder. The negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesocarbon microbeads, lithium titanate, silicon carbon, and silicon dioxide.

[0099] For example, the diaphragm is a material with polypropylene as the base material, or a rubber-coated diaphragm with ceramic coated on one side or both sides.

[0100] The lithium-ion battery of the present application is suitable for high-voltage systems, and includes a lithium-ion button battery with the aforementioned positive electrode sheet. Under the condition of ≥4.55V (relative to lithium), the positive electrode sheet has a gram capacity of ≥225mAh / g, and has excellent cycle performance at ≥4.50V (corresponding to the aforementioned negative electrode sheet).

[0101] Therefore, the lithium-ion battery of the present application has good cycle stability and high gram capacity at higher voltages such as 4.50V, which can meet the demand for lightweight and thin use of high-end digital products.

[0102] The technical solution of the present application will be further explained below with reference to specific embodiments.

[0103] Example 1

[0104] The positive electrode active material of this embodiment was prepared according to the following method:

[0105] (1) 38.153 g of sodium carbonate powder, 1.854 g of boric acid powder, 276.498 g of cobalt nitrate hexahydrate powder, and 1.020 g of nano-alumina powder were placed in a high-speed mixing device. The mixing program was set to 300 rpm for 3 minutes, 500 rpm for 5 minutes, and 1000 rpm for 10 minutes. The mixture was taken out and confirmed to be uniform after no white sodium carbonate spots were present in the mixture.

[0106] (2) Take about 30g of the mixed material and evenly put it into a ceramic crucible. Use a pit-type muffle furnace with the equipment model VBF-1200X for high-temperature sintering. The sintering temperature rise curve is 5℃ / min. When the temperature is raised to 780℃, it is sintered at a constant temperature for 10h. After sintering, the sample is naturally cooled to room temperature and then taken out. The sodium metal oxide Na is detected by inductively coupled plasma spectrometer (ICP). 0.72 Co 0.95 B 0.03 Al 0.02 O2;

[0107] (3) Weigh 10.49 g of lithium hydroxide monohydrate and 17.24 g of lithium nitrate particles in a reaction container, add the two lithium compounds into the reaction container, weigh 10 g of Na2O3 synthesized in step (2), and 0.72 Co 0.95 B 0.03 Al 0.02 O2 was poured into the reaction vessel and initially mixed, and then ion exchanged at 280 °C for 0.5 h to obtain a crude product;

[0108] (4) The crude product was filtered and washed with deionized water three times, and then dried at 90°C for 8 h to obtain sample 1A. The chemical formula of 1A was Li 0.715 Na 0.002 Co 0.95 B 0.03 Al 0.02 O2;

[0109] (5) Weigh 5 g of the sample 1A powder obtained in step (4) and place it in the reaction chamber of the ALD reaction equipment. The reaction temperature is controlled to 290°C. Lithium tert-butoxide, trimethylaluminum, titanium tetrachloride, and trimethylphosphine are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of 1A with 150 interval pulses, thereby forming an intermediate positive electrode active material 1B having a first coating layer. TEM testing is performed on 1B. Figure 2 is a TEM image of the intermediate positive electrode active material 1B in Example 1 of the present application. As shown in Figure 2, the thickness of the first coating layer is 10 to 12 nm.

[0110] (6) 3.5 g of sample 1B and 8.75 mg of selenium powder were weighed and mixed in a small high-speed mixer for 10 minutes. The mixture was then placed in a corresponding VBF-1200X muffle furnace and sintered at 300°C for 15 minutes to obtain the positive electrode active material 1C of this embodiment. 1C was subjected to TEM testing. Figure 3 is a TEM image of the positive electrode active material 1C of Example 1 of the present application. As shown in Figure 3 (wherein region A is the core, region B is the first coating layer, and region C is the second coating layer), it can be seen that the thickness of the second coating layer is 17 to 20 nm.

[0111] The relevant preparation parameters during the preparation process are shown in Table 1.

[0112] Example 2

[0113] The preparation method of the positive electrode active material of this embodiment is basically the same as that of Example 1, except that: in step (5), 5 g of sample 1A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature is controlled to 290°C. Lithium tert-butoxide, trimethylaluminum, titanium tetrachloride, and trimethylphosphine are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of 1A with 100 interval pulses, thereby forming an intermediate positive electrode active material 2B having a first coating layer. TEM analysis of sample 2B shows that the thickness of the first coating layer is 8 to 9 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0114] Example 3

[0115] The preparation method of the positive electrode active material of this embodiment is basically the same as that of Example 1, except that: in step (5), 5g of sample 1A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature is controlled to 290°C. Lithium tert-butoxide, trimethylaluminum, titanium tetrachloride, and trimethylphosphine are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of 1A with 80 interval pulses, thereby forming an intermediate positive electrode active material 3B having a first coating layer. TEM analysis of sample 3B shows that the thickness of the first coating layer is 6-7nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0116] Example 4

[0117] The preparation method for the positive electrode active material of this embodiment is substantially the same as that of Example 1, except that step (6) involves weighing 3.5 g of sample 1B and 7.0 mg of selenium powder, mixing them in a small high-speed mixer for 10 minutes, then placing the mixture in a corresponding VBF-1200X muffle furnace and sintering at 300°C for 15 minutes to obtain the positive electrode active material 4C of this embodiment. TEM analysis of sample 4C revealed that the coating thickness was 14 to 16 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0118] Example 5

[0119] The preparation method for the positive electrode active material of this embodiment is substantially the same as that of Example 1, except that step (6) involves weighing 3.5 g of sample 1B and 10.5 mg of selenium powder, mixing them in a small high-speed mixer for 10 minutes, then placing the mixture in a corresponding VBF-1200X muffle furnace and sintering at 300°C for 15 minutes to obtain the positive electrode active material 5C of this embodiment. TEM analysis of sample 5C revealed that the thickness of the second coating layer was 25 to 30 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0120] Example 6

[0121] The preparation method of the positive electrode active material of this embodiment is basically the same as that of Example 1, except that:

[0122] In step (1), 38.153 g of sodium carbonate powder, 1.96 g of phosphoric acid powder, 276.498 g of cobalt nitrate hexahydrate powder, and 1.529 g of nano-alumina powder were taken and placed in a high-speed mixing device. The mixing program was set to mix at 300 rpm for 3 minutes, then at 500 rpm for 5 minutes, and then at 1000 rpm for 10 minutes. After taking out the mixture, it was confirmed that there were no white spots of sodium carbonate in the mixture, and the mixture was considered uniform;

[0123] The sodium metal oxide obtained in step (2) is Na 0.72 Co 0.95 Al 0.03 P 0.02 O2;

[0124] After treatment in step (4), sample 6A was obtained, whose chemical formula is Li 0.717 Na 0.003 Co 0.95 Al 0.03 P 0.02 O2;

[0125] After treatment in step (5), sample 6B was obtained.

[0126] After processing in step (6), sample 6C was obtained. The relevant preparation parameters in the preparation process are shown in Table 1.

[0127] Example 7

[0128] The preparation method of the positive electrode active material of this embodiment is substantially the same as that of Example 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of an ALD reaction apparatus. The reaction temperature is controlled at 290°C. Lithium tert-butoxide, triethyl borate, and deionized water are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of the lithium metal oxide with 150 pulse intervals, thereby forming an intermediate positive electrode active material 7B having a first coating layer. TEM analysis of sample 7B shows that the thickness of the first coating layer is 11 to 13 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0129] Example 8

[0130] The preparation method of the positive electrode active material of this embodiment is substantially the same as that of Example 6, except that in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of an ALD reactor. The reaction temperature is controlled at 220°C, trimethylaluminum and deionized water are introduced into the reaction chamber using an inert gas as a carrier gas, and atomic layer vapor deposition is performed on the surface of the lithium metal oxide with 150 pulse intervals, thereby forming an intermediate positive electrode active material 8B having a first coating layer. TEM analysis of sample 8B shows that the thickness of the first coating layer is 11 to 13 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0131] Example 9

[0132] The preparation method of the positive electrode active material of this embodiment is substantially the same as that of Example 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature is controlled at 220°C. Magnesium bismuth and deionized water are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of the lithium metal oxide with 150 pulse intervals, thereby forming an intermediate positive electrode active material 9B having a first coating layer. TEM analysis of sample 9B shows that the thickness of the first coating layer is 11 to 13 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0133] Example 10

[0134] The preparation method for the positive electrode active material of this embodiment is substantially the same as that of Example 1, except that step (6) involves weighing 3.5 g of sample 1B and 35 mg of selenium powder, mixing them in a small high-speed mixer for 10 minutes, then placing the mixture in a corresponding VBF-1200X muffle furnace and sintering at 300°C for 15 minutes to obtain the positive electrode active material 10C of this embodiment. TEM analysis of sample 10C revealed that the thickness of the second coating layer was 120-125 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0135] Example 11

[0136] The preparation method of the positive electrode active material of this embodiment is basically the same as that of Example 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature is controlled at 290°C. Lithium tert-butoxide, lanthanum tris(N,N-diisopropylformamidinium) (LaFAMD), titanium tetrachloride, and deionized water are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of the lithium metal oxide with 150 pulse intervals, thereby forming an intermediate positive electrode active material 11B having a first coating layer. TEM analysis of sample 11B shows that the thickness of the first coating layer is 11 to 13 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0137] Example 12

[0138] The preparation method of the positive electrode active material of this embodiment is basically the same as that of Example 6, except that: in step (5), 5 g of sample 6A powder obtained in step (4) is weighed and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature is controlled at 290°C. Lithium tert-butoxide, tris(N,N-diisopropylformamidinium) lanthanum (LaFAMD), tetrakis(dimethylamino)zirconium (TDMAZ), and deionized water are introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition is performed on the surface of the lithium metal oxide with 150 pulse intervals, thereby forming an intermediate positive electrode active material 12B having a first coating layer. TEM analysis of sample 12B shows that the thickness of the first coating layer is 11 to 13 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0139] Example 13

[0140] The preparation method for the positive electrode active material of this embodiment is substantially the same as that of Example 1, except that step (6) involves weighing 3.5 g of sample 1B and 8.75 mg of lithium-selenium alloy powder, mixing them in a small high-speed mixer for 10 minutes, then placing the mixture in a corresponding VBF-1200X muffle furnace and sintering at 300°C for 15 minutes to obtain the positive electrode active material 13C of this embodiment. TEM analysis of the 13C sample revealed that the thickness of the second coating layer was 17 to 20 nm. The relevant preparation parameters during the preparation process are shown in Table 1.

[0141] Example 14

[0142] The preparation method of the positive electrode active material of this embodiment is substantially the same as that of Example 1, except that the order of steps 5) and 6) in Example 1 is reversed to obtain positive electrode active material 14C of Example 14. Relevant preparation parameters during the preparation process are shown in Table 1.

[0143] Example 15

[0144] The preparation method of the positive electrode active material of this embodiment is basically the same as that of Example 1, except for the ALD coating temperature and the number of pulses in step (5). The relevant preparation parameters during the preparation process are shown in Table 1.

[0145] Example 16

[0146] The preparation method of the positive electrode active material of this embodiment is substantially the same as that of Example 1, except that step (5) is omitted and step (6) is performed directly after step (4) to obtain the positive electrode active material of Example 16. The relevant preparation parameters during the preparation process are shown in Table 1.

[0147] Comparative Example 1

[0148] The positive electrode active material of this comparative example includes a conventional high voltage doped lithium cobalt oxide positive electrode material, and its chemical composition 10A sample is Li 1.0027 Co 0.97 Al 0.03 O2.

[0149] The above-mentioned lithium cobalt oxide positive electrode material 10A was weighed 5 g according to step (5) of Example 1 and placed in the reaction chamber of the ALD reaction equipment. The reaction temperature was controlled to 290°C. Lithium tert-butoxide, trimethylaluminum, titanium tetrachloride, and trimethylphosphine were introduced into the reaction chamber using an inert gas as a carrier gas. Atomic layer vapor deposition was performed on the surface of the lithium metal oxide with 150 interval pulses, thereby forming a material 10B having a first coating layer. TEM testing of the 10B sample showed that the thickness of the first coating layer was 10 to 12 nm.

[0150] (6) 3.5 g of sample 10B and 8.75 mg of selenium powder were weighed and mixed in a small high-speed mixer for 10 min. The mixture was then placed in a VBF-1200X muffle furnace and sintered at 300°C for 15 min to obtain the positive electrode active material 10C of Comparative Example 1. TEM analysis of sample 10C revealed that the thickness of the second coating layer was 17-20 nm. The relevant preparation parameters are shown in Table 1.

[0151] Comparative Example 2

[0152] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that the treatments in steps (5) and (6) are not performed, and the 1A sample obtained in step (4) is directly used as the positive electrode active material of Comparative Example 2. The relevant preparation parameters during the preparation process are shown in Table 1.

[0153] Comparative Example 3

[0154] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that the treatment in step (6) is omitted and the 1B sample obtained in step (5) is directly used as the positive electrode active material of Comparative Example 3. The relevant preparation parameters during the preparation process are shown in Table 1.

[0155] Test Example 1

[0156] TEM and ICP tests were performed on the positive electrode active materials obtained from all examples and comparative examples to determine the coating thickness, chemical composition, and Se content. TEM tests were also performed on the intermediate positive electrode active material that had undergone the first coating treatment to determine the thickness of the first coating layer. The results are shown in Table 1.

[0157] Test Example 2

[0158] XRD diffraction was performed on the positive electrode active materials obtained in all examples and comparative examples, and the 2θ values ​​of the 002 peak and 131 peak corresponding to the XRD patterns are shown in FIG5 , FIG6 and Table 2.

[0159] Test Example 3

[0160] After the positive electrode active materials obtained in all the examples and comparative examples are made into positive electrode sheets, they are assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain lithium-ion batteries. The method includes:

[0161] 1) The positive electrode active materials of the examples and comparative examples were mixed with conductive carbon black and PVDF at a weight ratio of 96%:2%:2% respectively, and a positive electrode slurry was prepared by dispersion. The slurry was coated on an aluminum foil current collector and roll-pressed to prepare a positive electrode sheet.

[0162] 2) Artificial graphite, styrene diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black are mixed in a weight ratio of 94%:3%:2%:1%. The mixture is dispersed in water and mixed using a double planetary mixer to produce a negative electrode slurry. This slurry is then coated onto a copper current collector, followed by roller pressing and drying.

[0163] Then, a lithium material layer is superimposed on the surface of the negative electrode active layer by rolling. The lithium material layer is lithium foil, and the surface density of metallic lithium is 1.0 mg / cm 2 , and finally a negative electrode sheet containing lithium metal is obtained.

[0164] 3) The positive electrode sheet, negative electrode sheet and separator are then assembled into a lithium-ion battery and injected with non-aqueous electrolyte.

[0165] Among them, the electrolyte is a conventional electrolyte known in the art, which is mixed in a mass ratio of ethylene carbonate (abbreviated as EC): diethyl carbonate (abbreviated as DEC): propylene carbonate (abbreviated as PC) = 2:5:3, and then 5% of the total mass of the electrolyte is added with fluoroethylene carbonate (abbreviated as FEC), 13% of the total mass of the electrolyte is added with lithium hexafluorophosphate (abbreviated as LiPF6), and the additive shown in formula T, and the content of the additive accounts for 2% of the total content of the electrolyte.

[0166] The capacity retention rate of each lithium-ion battery obtained was tested. The specific test method was as follows: at 25°C, the battery was charged at a constant current of 1C to 4.50V, then charged at a constant voltage of 0.05C to 4.50V, and then discharged at a discharge rate of 1C to 3.0V. This charge and discharge cycle was repeated 500 times. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were measured. The capacity retention rate after 500 cycles was calculated according to the following formula. The results are shown in Table 2.

[0167] Capacity retention rate Q = (discharge capacity at the 500th cycle) / (discharge capacity at the first cycle) * 100%

[0168] Test Example 4

[0169] After the positive electrode active materials obtained in all the examples and comparative examples are made into positive electrode sheets, they are assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain button batteries. The method includes:

[0170] The positive electrode active materials from the examples and comparative examples were mixed with conductive carbon black (SP) and PVDF at a weight ratio of 80%:10%:10%, respectively, to form a positive electrode slurry. This slurry was coated onto an aluminum foil current collector and roll-pressed to produce a positive electrode sheet. The positive electrode sheet was then punched into a small disc with a diameter of 12 mm using a mold. After drying and weighing, the positive electrode sheet was assembled into a button cell in a glove box under an Ar atmosphere using a 2025 coin cell case, a lithium metal disc as the negative electrode, and a conventional high-voltage lithium cobalt oxide electrolyte.

[0171] After each button cell was left to stand for 4 hours under normal conditions, the first charge and discharge capacity test was carried out. The test conditions were as follows: 0.1C charging to 4.55V, constant voltage charging to 0.025C and then cutting off, standing for 3 minutes, and then 0.1C discharging to 3.0V. During the discharge process, the discharge capacity C1 at 4.4-4.55V, the discharge capacity C2 at 3.7-3.8V, the first discharge full capacity C0, and the first charge gram capacity were recorded respectively, and the first efficiency, the first stage discharge capacity ratio C1 / C0, and the second stage discharge capacity ratio C2 / C0 were calculated. The results are shown in Table 2. Figure 4 is the charge and discharge curve of the button cell obtained by assembling the positive electrode active material of Example 1 of the present application.

[0172] Table 1

[0173] Table 2

[0174] According to Table 2, the positive electrode active material of the present application is beneficial to improving the discharge capacity and cycle performance of lithium-ion batteries.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode active material, wherein The positive electrode active material includes a matrix and a coating layer covering at least a part of the surface of the matrix; wherein, the matrix includes a lithium metal oxide represented by Formula 1 and / or Formula 2, and the coating layer includes selenium element; Li n1-y1 Na y1 Co e1 M1 b1 M2 a1 O2 Formula 1 Li n2-y2-b2 Na y2 Co e2 M1 b2 M2 a2 O2 Formula 2 In Formula 1, 0.6≤n1≤1.0, 0<y1≤0.05, 0.8≤e1≤1.03, 0≤a1≤0.1, 0<b1≤0.1, 0<b1 / 1-a1-b1<0.1; in Formula 2, 0.6≤n2≤1.0, 0<y2≤0.05, 0.8≤e2≤1.03, 0≤a2≤0.1, 0<b2≤0.02; in Formula 1 and Formula 2, M1 is selected from at least one of Te, W, Al, B, P, Se, Ti, La, Zr, and K; M2 is a doping element different from M1; The lithium metal oxide is in the Cmca space group of the cubic crystal system, and has a 002 peak with 2θ of 17.9° - 18.1° and a 131 peak with 2θ of 67.0° - 67.5°.

2. The positive electrode active material according to claim 1, wherein The coating layer includes a first coating layer and a second coating layer in the direction away from the matrix; the first coating layer includes at least one of a metal compound and the selenium element, and the second coating layer includes at least one of a metal compound and the selenium element; Preferably, the compositions of the first coating layer and the second coating layer are different.

3. The positive electrode active material according to claim 2, wherein The first coating layer includes a metal compound, and the second coating layer includes selenium element; Or, the first coating layer includes selenium element, and the second coating layer includes a metal compound.

4. The positive electrode active material according to any one of claims 1 to 3, wherein The coating layer containing the selenium element is a selenium single element layer or a selenium-metal alloy layer.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The mass percentage content of selenium element in the positive electrode active material is less than 5000 ppm.

6. The positive electrode active material according to any one of claims 2 to 5, wherein: The metal compound includes at least one of a lithium-containing oxide, an aluminum-containing oxide, a magnesium-containing oxide, a zirconium-containing oxide, and a titanium-containing oxide.

7. The positive electrode active material according to claim 6, wherein The lithium ion conductivity of the lithium-containing oxide is greater than or equal to 1×10 -3 S / cm; And / or, the lithium-containing oxide includes at least one of LATP, LLTO, LLZO, Li3BO3, and Li3PO4.

8. The positive electrode active material according to claim 2 or 3, wherein The thickness of the first coating layer is not greater than 20 nm; and / or, the thickness of the second coating layer is not greater than 100 nm.

9. The positive electrode active material according to claim 1, wherein The Dv50 of the matrix is 12 - 18 μm; and / or, M2 includes at least one of Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B, and P elements.

10. A positive electrode sheet, wherein: The positive electrode sheet includes the positive electrode active material according to any one of claims 1 - 9.

11. The positive electrode sheet according to claim 10, wherein: Under the condition that the positive electrode sheet is ≥4.55V in a coin cell, the specific capacity of the positive electrode sheet is ≥225 mAh / g.

12. A lithium ion battery, wherein: The lithium ion battery includes the positive electrode active material according to any one of claims 1 - 9 or the positive electrode sheet according to claim 10.

13. The lithium ion battery according to claim 12, wherein: The working voltage of the lithium ion battery is greater than or equal to 4.5V.

14. The lithium ion battery according to claim 12 or 13, wherein: The lithium ion battery further includes a negative electrode sheet, and the negative electrode sheet includes a lithium-containing layer.

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