A positive electrode active material and use thereof

Abstract

This invention provides a positive electrode active material and its application. The positive electrode active material includes a lithium metal oxide as shown in Formula 1 or Formula 2. In the X-ray diffraction pattern, the lithium metal oxide has a cubic crystal system with space group Cmca and has a 002 peak with a 2θ of 17.9°–18.1° and a 131 peak with a 2θ of 67.0°–67.5°. In Formula 1 and Formula 2, M1 is selected from at least one of Te, W, Al, B, P, and K; M2 is a doping element different from M1. The positive electrode active material of this invention is beneficial for improving the cycle performance and specific capacity of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to an electrode material, and more particularly to a positive electrode active material and its application, belonging to the field of secondary battery technology. Background Technology

[0002] With the development and advancement of lithium-ion battery technology, increasingly higher demands are being placed on its capacity. In the composition of a lithium-ion battery, the capacity of the positive electrode active material plays a crucial role in the battery's overall capacity.

[0003] To increase the capacity of lithium-ion batteries, the most common method 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 reduction in cycle performance.

[0004] Therefore, developing a positive electrode active material for lithium-ion batteries with high specific capacity and good cycle performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention provides a positive electrode active material whose special composition and crystal phase structure help improve the specific capacity and cycle performance of the battery, especially under high voltage conditions, it can still enable the battery to perform well.

[0006] The present invention provides a positive electrode sheet comprising the above-mentioned positive electrode active material, which helps to improve the relevant electrical performance of the battery.

[0007] The present invention also provides a lithium-ion battery comprising the above-mentioned positive electrode, thereby exhibiting excellent performance in terms of specific capacity and cycle performance.

[0008] This invention provides a positive electrode active material, wherein the positive electrode active material comprises lithium metal oxide as shown in Formula 1 or Formula 2;

[0009] In the X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system in space group Cmca, 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°.

[0010] Li n1-y1 Na y1 Co 1-a1-b1 M1 b1 M2 a1 O2 Formula 1

[0011] Li n2-y2-b2 Na y2 Co 1-a2 M1 b2 M2a2 O2 Formula 2

[0012] In Equation 1, 0.6 ≤ n1 ≤ 0.8, 0 < y1 ≤ 0.05, 0 ≤ a1 ≤ 0.1, 0 < b1 ≤ 0.1, 0 <b1 / 1-a1-b1<0.1;

[0013] In Equation 2, 0.6 ≤ n² ≤ 0.8, 0 < y² ≤ 0.05, 0 ≤ a² ≤ 0.1, 0 < b² ≤ 0.02.

[0014] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a dopant element.

[0015] The positive electrode active material as described above, wherein, in Formula 1, M1 is selected from one of Al, W and / or Te, B and / or P;

[0016] In Equation 2, M1 is K.

[0017] The positive electrode active material as described above, wherein the positive electrode active material is composed of a core including the lithium metal oxide and a coating layer covering at least a portion of the surface of the core.

[0018] The positive electrode active material as described above, wherein when the cutoff voltage is 3.0 to 3.6V and the SOC is zero, 0.7 ≤ n1 and n2 ≤ 1.0.

[0019] The positive electrode active material as described above, wherein the median particle size of the positive electrode active material is 12 μm to 20 μm.

[0020] The positive electrode active material as described above, wherein,

[0021] The first-stage discharge capacity ratio of the positive electrode active material is C1 / C0≥9%, and the second-stage discharge capacity ratio is C2 / C0≥25%.

[0022] Wherein, C0 is the discharge capacity of the half-cell including the positive electrode active material when it is discharged at a voltage of 3.0 to 4.55V; in the discharge process, the capacity released by the half-cell when it is discharged from the initial discharge voltage to 4.4V is defined as C1, and the capacity released by the half-cell when it is discharged from 3.8V to 3.7V is defined as C2.

[0023] In the positive electrode active material described above, the peak intensity of the 002 peak is I1, the peak intensity of the 131 peak is I2, and I1 / I2≥4.

[0024] The present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode active material described in any of the above claims.

[0025] The present invention provides a lithium-ion battery, the lithium-ion battery comprising the positive electrode sheet as described above.

[0026] The lithium-ion battery described above, wherein the negative electrode in the lithium-ion battery is a lithium-containing negative electrode.

[0027] The positive electrode active material of the present invention has a special crystal phase structure and chemical composition. When applied to batteries, the cycle performance and specific capacity of the batteries are significantly improved. Even under high voltage conditions of 4.5V and above, batteries using this positive electrode active material can still maintain excellent electrical performance and will not experience structural collapse due to poor voltage resistance of the positive electrode active material. Attached Figure Description

[0028] Figure 1 This is a partial structural schematic diagram of an embodiment of the negative electrode sheet in the lithium-ion battery of the present invention;

[0029] Figure 2 The image shown is the XRD pattern of sample 1A# in Example 1A of this invention.

[0030] Figure 3 This is a SEM image of sample 1C# in Example 1C of the present invention;

[0031] Figure 4 This is a SEM image of sample 3C# in Embodiment 3C of the present invention;

[0032] Figure 5 The curves show the comparison of the cycling performance of sample 1D# in Example 1D of the present invention and the sample in Comparative Example 3. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] The first aspect of the present invention provides a positive electrode active material, the positive electrode active material comprising lithium metal oxide as shown in Formula 1 or Formula 2;

[0035] In the X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system in space group Cmca, 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°.

[0036] Li n1-y1 Na y1 Co1-a1-b1 M1 b1 M2 a1 O2 Formula 1

[0037] Li n2-y2-b2 Na y2 Co 1-a2 M1 b2 M2 a2 O2 Formula 2

[0038] In Equation 1, 0.6 ≤ n1 ≤ 0.8, 0 < y1 ≤ 0.05, 0 ≤ a1 ≤ 0.1, 0 < b1 ≤ 0.1, 0 <b1 / 1-a1-b1<0.1;

[0039] In Equation 2, 0.6≤n2≤0.8, 0<y2≤0.05, 0≤a1≤0.1, 0<b2≤0.02;

[0040] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1.

[0041] The lithium metal oxide described above in this invention is a compound having a T2 phase stacking structure, specifically an oxide comprising at least lithium, sodium, and M1. Furthermore, it may be doped with M2. This invention does not limit the specific selection of M2 and it can be a common doping element in the art. For example, it can be at least one of the elements Mg, Ti, Mn, Al, Te, W, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B, and P.

[0042] This invention does not impose excessive restrictions on y1, y2, a1, a2, b1, b2, etc. within the above-mentioned scope.

[0043] For example, in Equation 1, y1 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; a1 is 0.001, 0.002, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.0 65, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; b1 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0. 030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; b1 / 1-a1-b1 is 0.005, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08, 0.09, 0.095, or 0.1.

[0044] In Equation 2, y2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.03, 0.04, or 0.05; a2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, 0.05, 0.018, 0.012, 0.015, 0.018, 0.012, 0.015, 0.018, 0.012, 0.015, 0.018, 0.012, 0.015, 0.012, 0.015, 0.012, 0.013, 0.014 ... .020, 0.022, 0.024, 0.025, 0.026, 0.028, 0.030, 0.032, 0.034, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, or 0.095; b2 is 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.010, 0.012, 0.015, 0.018, or 0.02. a2 / 1-a2 is 0.005, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08, 0.09, 0.095 or 0.1.

[0045] It is important to emphasize that the above-mentioned limitations on n1 and n2 refer to the molar amount of lithium per mole of lithium metal oxide in the positive electrode active material before any charge-discharge treatment. It is understandable that when this positive electrode active material is applied to a lithium-ion battery and subjected to any charge-discharge treatment, the molar amount of lithium per mole of lithium metal oxide will vary under different charge-discharge mechanisms and at different charge-discharge nodes.

[0046] According to the above-described solution provided by the present invention, compared with other positive electrode active materials, the application of the positive electrode active material including this lithium metal oxide to a lithium-ion battery significantly improves the specific capacity and cycle performance of the lithium-ion battery. Even under high-voltage operating conditions, the electrical performance of the lithium-ion battery does not deteriorate. Based on this phenomenon, the inventors analyzed it and believe that it may be due to the following: On the one hand, the doping of M1 helps to support the structure of the lithium metal oxide, thereby improving the structural stability of the lithium metal oxide to a certain extent. Therefore, regardless of whether it is an atmospheric pressure or a high-pressure operating environment, the structurally stable lithium metal oxide is more conducive to improving the efficiency of lithium-ion insertion and extraction, and promoting the improvement of the cycle performance and specific capacity of the lithium-ion battery. On the other hand, the lithium metal oxide with the above-described crystal characteristics has a more complete layered crystal phase structure, which reduces or suppresses the occurrence of internal mixing phenomena in the crystal phase, thereby enabling lithium-ion insertion and extraction to occur smoothly, especially exhibiting multiple small charge and discharge plateaus during high-pressure charge and discharge processes.

[0047] Furthermore, M1 in Formula 1 is selected from Al, W and / or Te, B and / or P (i.e., M1 is selected from any one of Al, W, Te, blends of W and Te, B, P, and blends of B and P); M1 in Formula 2 is K. Specifically, when M1 in Formula 1 and Formula 2 is selected from different doping elements, the degree of improvement in the relevant electrical properties of lithium metal oxides varies to some extent.

[0048] In detail, when M1 in Formula 1 contains one of Al, Te and / or W, P, it is speculated that Al atoms, Te atoms and / or W atoms, P atoms can replace Co atoms in lithium metal oxide, thereby improving the structural stability of lithium metal oxide, enabling lithium metal oxide under high voltage to successfully complete the insertion and extraction of lithium ions without structural collapse, thus improving the specific capacity and cycle performance of the battery.

[0049] When M1 in Formula 1 contains B atoms, the insertion of B atoms can replace Co atoms in lithium metal oxide, which has a certain degree of fluxing effect and helps to make lithium metal oxide a single crystal morphology (i.e., primary particles), thereby increasing the compaction density of the positive electrode.

[0050] When M1 in Equation 2 is selected from K atoms, it is speculated that the radius of K atoms is larger than that of Li and Na atoms. In lithium metal oxides, K atoms occupy sites and provide support, which is conducive to the insertion and extraction of Li ions, thereby significantly improving cycle performance and specific capacity. In addition, by controlling the amount of K doping, the electrochemical kinetics and rate performance during battery charging and discharging can be improved, and polarization can be reduced, which also has a positive promoting effect on rate performance and first-efficiency.

[0051] In addition to the positive effects of lithium metal oxide on battery-related electrical performance, the battery performance is further improved when a coating layer is applied to at least a portion of the surface of the lithium metal oxide. By incorporating the coating layer, the positive electrode active material has a core-shell structure comprising a lithium metal oxide core and a coating layer covering the core. This coating layer helps reduce or suppress side reactions between the lithium metal oxide and the electrolyte. Even when the battery operates under high voltage, a stable interface can still be formed between the positive electrode active material and the electrolyte, improving the battery's cycle performance by preventing excessive dissolution of metal ions from the positive electrode active material and avoiding electrolyte shortage. Simultaneously, the suppression or reduction of side reactions also reduces gas production within the battery, thereby ensuring battery safety.

[0052] This invention does not limit the choice of coating material, as long as it can suppress side reactions and ensure the normal migration of lithium ions. To further improve lithium-ion conductivity, the coating material can be made of carbon-containing compounds, fast ion conductors, or other similar materials.

[0053] As mentioned earlier, in lithium metal oxides without any charge / discharge treatment, n1 and n2 are between 0.6 and 0.8. When a positive electrode sheet including the positive electrode active material and a lithium metal negative electrode sheet are assembled into a battery and then charged and discharged, when the battery's remaining charge (SOC) is 0 (i.e., in a fully discharged state) and the discharge cutoff voltage is 3.0–3.6V, n1 and n2 of the lithium metal oxide are between 0.7 and 1.0. It should be noted that these changes in n1 and n2 refer to a charge / discharge cycle count within 10. Specifically, after the aforementioned lithium metal oxides undergo charge / discharge applications, their composition changes, especially the molar amount of lithium increases significantly. This is because lithium metal oxides with the aforementioned crystal structure have some vacancies. Therefore, when they undergo charge / discharge treatment (e.g., formation), these vacancies can accept lithium atoms from the lithium negative electrode, thereby increasing the molar amount of lithium ions compared to before charge / discharge applications. This characteristic helps to further improve the battery's cycle performance and specific capacity.

[0054] The detection of n1 and n2 can be performed by ICP. Specifically, the discharged battery is disassembled and the positive electrode is removed. After soaking in dimethyl carbonate (DMC) for 1-3 hours or rinsing with DMC, the electrode is naturally dried in a drying room, then calcined in a muffle furnace at 300-600℃ for 2-5 hours. The powder to be tested is obtained by sieving through a 200-mesh sieve. Subsequently, the metal elements in the powder to be tested are detected by ICP, and n1 and n2 are calculated.

[0055] The positive electrode active material of the present invention can be single-crystal or polycrystalline, and the specific morphology is related to the selection and proportion of its doping elements. Specifically, when it is polycrystalline, it is spherical or near-spherical particles; when it is single-crystal, it can be whisker-like, plate-like, or other arbitrary irregular shapes.

[0056] Furthermore, the median particle size of the positive electrode active material of the present invention is 12–20 μm, for example, 3 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. The inventors have discovered that when the median particle size of the positive electrode active material meets the above requirements, on the one hand, its corresponding specific surface area can accommodate more lithium ion insertion / extraction; on the other hand, the agglomeration phenomenon between positive electrode active materials is effectively controlled, thereby enabling stable dispersion in the slurry during the slurry preparation process.

[0057] The inventors discovered that when lithium metal oxides meet the doping requirements of a specific element M1 and the doping ratio, multiple discharge plateaus during the charging and discharging process exhibit superior discharge capacity.

[0058] In one specific embodiment, the first-stage discharge capacity ratio of the positive electrode active material is C1 / C0 ≥ 9%, and the second-stage discharge capacity ratio is C2 / C0 ≥ 25%; wherein, C0 is the discharge capacity of the half-cell including the positive electrode active material when discharged at a voltage of 3.0–4.55V; in the discharge treatment, the discharge capacity of the half-cell from the initial discharge voltage to 4.4V is defined as C1, and the discharge capacity of the half-cell from 3.8V to 3.7V is defined as C2. Further, C1 / C0 ≥ 11%, and the second-stage discharge capacity ratio is C2 / C0 ≥ 28%.

[0059] It should be explained that the above discharge capacity is achieved under a specific discharge mechanism. Specifically, after the half-cell, consisting of a positive electrode sheet containing positive electrode active material and a lithium metal negative electrode, is charged to 100% SOC (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. The amount of electricity released during the voltage reduction phase from 3.8V to 3.7V is C2. The total amount of electricity initially released during the self-discharge when discharging to 3.0V (at which point the SOC is 0) is C0.

[0060] Clearly, in the discharge process under high-voltage conditions, both the first-stage discharge capacity ratio and the second-stage discharge capacity ratio exhibit excellent performance. Therefore, the positive electrode active material, including the lithium metal oxide of this invention, has strong voltage resistance, thereby enabling the specific capacity of the battery to be increased by performing a voltage boosting process.

[0061] In one embodiment, in the lithium metal oxide, the peak intensity of peak 002 is I1, the peak intensity of peak 131 is I2, and I1 / I2 ≥ 4. At this point, the internal crystal structure of the lithium metal oxide is more complete, thus contributing to improved battery cycle performance. Further, I1 / I2 ≥ 6.

[0062] The present invention does not limit the preparation method of the above-mentioned lithium metal oxide. In one specific embodiment, the lithium metal oxide of the present invention can be prepared by mixing the sodium metal oxide shown in formula 1a or 2a with a lithium compound and performing ion treatment.

[0063] Na x1 Co 1-a1-b1 M1 b1 M2 a1 O2 Formula 1a Na x2 Co 1-a2 M1 b2 M2 a1 O2 Formula 2a

[0064] In Formula 1a, 0.68 < x1 < 0.74, 0 < b1 < 0.1, 0 ≤ a < 0.10, 0 < b1 / (1 - a1) < 0.05; in Formula 2a, 0.68 < x2 < 0.74, 0 < b2 < 0.02, 0 ≤ a2 < 0.1.

[0065] The above ion exchange treatment is a heat treatment process, specifically referring to mixing sodium metal oxide and lithium compound and performing heat treatment at 80°C to 300°C for no more than 10 h. After the ion exchange treatment, the ion-exchanged system is washed and dried to finally obtain lithium metal oxide. Among them, the drying temperature is 80 to 180°C, and the time is at least 10 h. There is no limitation on the equipment for ion exchange treatment and 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 disk dryer, an oven, etc.

[0066] The above 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. In 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.

[0067] Furthermore, when preparing a cathode active material with a coating layer covering the lithium metal oxide, in the ion exchange treatment, in addition to the raw materials of sodium metal oxide and lithium compound, a coating layer raw material needs to be added.

[0068] For the sodium metal compounds shown in Formula 1a and Formula 2a,示例性, they can be prepared by a method including the following process:

[0069] Mix a cobalt source, a sodium source, an M1 source, and an M2 source in a target ratio and then perform a calcination treatment to obtain the sodium metal compounds shown in Formula 1a and Formula 2a.

[0070] Specifically, the temperature of the calcination treatment is 700 to 900°C, the time is 8 to 50 h, and the calcination treatment can be carried out in an oxygen or air atmosphere. The equipment for the calcination treatment can be, for example, a high-temperature sintering equipment such as a muffle furnace, a tunnel furnace, a roller hearth kiln, a tube furnace, etc.

[0071] The mixing of the above various sources can be performed by a high-speed mixing equipment, a sand milling equipment, a ball milling equipment, a plow blade mixing equipment, an inclined mixing equipment, etc. It should be noted that if a sand milling equipment or a ball milling equipment is used and a solvent (water, ethanol or other solvent media) is added during the ball milling or sand milling process, the mixed system needs to be dried after the mixing treatment. Generally, the mixing time is not more than 4 h.

[0072] This invention does not limit the specific selection of the cobalt source, sodium source, M1 source, and M2 source. Exemplarily, the cobalt source is selected from one or more of cobalt hydroxide, cobalt tetroxide, doped cobalt tetroxide, cobalt suboxide, cobalt hydroxyl oxide, cobalt nitrate, and cobalt sulfate; the sodium source is selected from one or more of sodium carbonate, sodium nitrate, sodium hydroxide, sodium bicarbonate, and sodium sulfate; 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. One or more of aluminum nitrate, aluminum hydroxide, etc.; when M1 is B, the source of M1 is, for example, boric acid and / or sodium borate, etc.; when M1 is P, the source of M1 is, for example, phosphoric acid and / or sodium phosphate, etc.; when M1 is K, the source of M1 is, for example, one or more of potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, etc.; the source of M2 can be any compound containing M2, such as an oxide of M2, for example, one or more of basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthanum oxide, lanthanum fluoride, nickel oxide, niobium oxide, etc.

[0073] A second aspect of the present invention provides a positive electrode sheet comprising the positive electrode active material described in the first aspect above.

[0074] Based on the characteristics of the positive electrode active material in the first aspect, the positive electrode sheet of the present invention helps to improve the cycle performance and specific capacity of lithium-ion batteries.

[0075] In one specific embodiment, the positive electrode sheet of the present invention includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including the aforementioned positive active material.

[0076] It is understood that, in addition to the positive electrode active material, the positive electrode active layer also includes a conductive agent and a binder. For example, the positive electrode active layer comprises, by weight percentage, 70-99 wt% positive electrode active material, 0.5-15 wt% conductive agent, and 0.5-15 wt% binder; more specifically, it comprises 80-98 wt% positive electrode active material, 1-10 wt% conductive agent, and 1-10 wt% binder.

[0077] The selection of conductive agent and binder is not special and can be conventional in the field. 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 nanotube, single-walled carbon nanotube, multi-arm carbon nanotube, and carbon fiber, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and lithium polyacrylate (PAALi).

[0078] Furthermore, to enhance safety performance, a safety layer can be placed between the positive electrode active layer and the current collector. The safety layer is typically made of non-conductive safety materials, such as iron-containing compounds (e.g., lithium iron phosphate, lithium phosphate) or aluminum-containing compounds (e.g., ceramic alumina). Of course, the safety layer also includes a binder, and the ratio of binder to safety material can be further determined according to specific requirements.

[0079] A third aspect of the present invention also provides a lithium-ion battery comprising the above-described positive electrode, thereby exhibiting outstanding performance in terms of cycle performance and specific capacity.

[0080] This invention does not limit the specific structure of the lithium-ion battery; for example, it can be a square-shell battery, a cylindrical battery, etc.

[0081] According to the present invention, the lithium-ion battery further includes a negative electrode, a separator, and an electrolyte.

[0082] Exemplarily, the electrolyte is a conventional electrolyte known in the art, comprising a lithium salt and a solvent, wherein the solvent contains ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), or fluoroethylene carbonate (FEC). Further, it also includes an additive represented by Formula T, wherein the mass percentage of the additive in the electrolyte is 0.1% to 10%, etc.

[0083]

[0084] For example, the negative electrode can be a lithium metal-containing negative electrode, such as lithium foil or... Figure 1 The negative electrode shown. Specifically, Figure 1 The negative electrode sheet includes a negative electrode current collector 101, a negative electrode active layer 20 and a lithium material layer 30 stacked together. Figure 1 The negative electrode sheet is double-sided, but it can also be a negative electrode sheet with the negative electrode active layer 20 and the lithium material layer 30 only on one side of the negative electrode current collector. The lithium material layer is, for example, a lithium foil, and further, the areal density of metallic lithium in the lithium material layer is 0.09 mg / cm³. 2 ~3.5mg / cm 2 The negative electrode active layer includes negative electrode active material, conductive agent and binder.

[0085] In one specific embodiment, the negative electrode active layer comprises, by weight percentage, 70-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder; more specifically, it comprises 80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder. The negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbide, and silicon suboxide.

[0086] For example, the diaphragm is a polypropylene-based material, or a coated diaphragm with ceramic coating on one or both sides.

[0087] The lithium-ion battery of the present invention is suitable for high-voltage systems. Specifically, under the condition of ≥4.55V (relative to lithium) for the lithium-ion coin cell including the aforementioned positive electrode, the specific capacity of the positive electrode is ≥225mAh / g, and it also has excellent cycle performance at ≥4.50V (corresponding to the aforementioned negative electrode).

[0088] Therefore, the lithium-ion battery of the present invention has good cycle stability and high specific capacity at higher voltages such as 4.50V, which can meet the usage requirements of high-end digital products for thinner and lighter designs.

[0089] The positive electrode active material of the present invention will be described below through specific embodiments.

[0090] Example 1A

[0091] The positive electrode active material in this embodiment is prepared according to the following method:

[0092] (1) Weigh 36.56g of sodium carbonate powder, 6.889g of telluric acid powder, and 282.32g of cobalt nitrate hexahydrate powder, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. Take out the mixture and confirm that there are no white sodium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0093] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X well-type muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 750℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample. The sodium metal oxide Na was detected by inductively coupled plasma atomic emission spectrometry (ICP). 0.69 Co 0.97 Te 0.03 O2;

[0094] (3) Weigh 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate granules into a reaction vessel. Add the two lithium compounds separately into the reaction vessel. Weigh 10g of the Na synthesized in step (2). 0.69 Co 0.97 Te 0.03 O2 was poured into a reaction vessel and mixed initially, then ion exchanged at 280℃ for 0.5 h to obtain the crude product;

[0095] (4) After the crude product was washed by deionized water filtration three times, it was dried at 90℃ for 8 hours to obtain sample 1A#.

[0096] ICP was used to detect and analyze 1A#, and the specific results are shown in Table 1A.

[0097] Figure 2 This is the XRD pattern of sample 1A# in Embodiment 1A of the present invention. From... Figure 2 It can be seen that the lithium metal oxide prepared in this embodiment has a 002 peak and a 131 peak, and it is a cubic crystal system with the Cmca space group and has a T2 structure.

[0098] Examples 2A-9A

[0099] The preparation methods of Examples 2A-9A are basically the same as those of Example 1A, except that different M1 (W source or Te source), M2 source, and mass ratio between each metal source are selected in step (1). The specific selection is shown in Table 1A. Finally, samples 2A#-9A# are obtained, and their ICP detection and analysis results are shown in Table 1A.

[0100] Example 10A

[0101] The preparation method of Example 10A is basically the same as that of Example 1A, except that step (1) is as follows: weigh 36.56g of sodium carbonate powder, weigh 4.593g of telluric acid powder, and weigh 79.30g of the compound (Co) that has been doped with aluminum. 0.95 Al 0.03 )3O4 is placed in a high-speed mixing device, the mixing program is set, and the mixture is mixed 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 is considered that the mixture is uniform after confirming that there are no white sodium carbonate spots in the mixture.

[0102] The sodium metal oxide obtained in the final step 2) is Na 0.69 Co 0.95 Te 0.02 Al 0.03 O2 and sample 10A# is Li 0.71 Na 0.02 Co 0.95 Te 0.02 Al 0.03 O2.

[0103] Example 11A

[0104] The preparation method of Example 11A is basically the same as that of Example 10A, except that step (3) is as follows: 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate particles are weighed into a reaction vessel. The two lithium compounds are added to the reaction vessel separately. 10g of the Na synthesized in step (2) is weighed. 0.69 Co 0.95 Te 0.02 Al 0.03 O2 was poured into the reaction vessel and initially mixed, then ion exchanged at 280℃ for 1 hour to obtain the crude product; after processing in step (4), sample 11A#Li was obtained. 0.71 Na 0.02 Co 0.95 Te 0.02 Al 0.03 O2.

[0105] Example 12A

[0106] The preparation method of Example 12A is basically the same as that of Example 10A, except that step (3) is as follows: 10.49g of lithium hydroxide monohydrate and 9.24g of lithium carbonate particles are weighed into a reaction vessel. The two lithium compounds are added to the reaction vessel separately. 10g of the Na synthesized in step (2) is weighed. 0.69 Co 0.95 Te 0.02 Al 0.03 O2 was poured into the reaction vessel and initially mixed, then ion exchanged at 280℃ for 0.5 h to obtain the crude product; after treatment in step (4), sample 12A#Li was obtained. 0.71 Na 0.0.02 Co 0.95 Te 0.02 Al 0.03 O2.

[0107] Example 13A

[0108] The preparation method of Example 13A is basically the same as that of Example 10A, except that step (3) is as follows: 10.49g of lithium hydroxide monohydrate and 10.59g of lithium chloride particles are weighed into a reaction vessel. The two lithium compounds are added to the reaction vessel separately. 10g of the Na synthesized in step (2) is weighed. 0.69 Co 0.95 Te 0.02 Al 0.03 O2 was poured into the reaction vessel and initially mixed, then ion exchanged at 280℃ for 0.5 h to obtain the crude product; after treatment in step (4), sample 13A#Li was obtained. 0.71 Na0.0.02 Co 0.95 Te 0.02 Al 0.03 O2.

[0109] Table 1A

[0110]

[0111]

[0112] Example 1B

[0113] The positive electrode active material in this embodiment is prepared according to the following method:

[0114] (1) Weigh 36.56g of sodium carbonate powder, 1.53g of nano alumina powder, 276.50g of cobalt nitrate hexahydrate powder and 0.806g of nano magnesium oxide powder, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. Take out the mixture and confirm that there are no white sodium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0115] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X well-type muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 750℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample. The sodium metal oxide Na was detected by inductively coupled plasma atomic emission spectrometry (ICP). 0.69 Co 0.95 Al 0.03 Mg 0.02 O2;

[0116] (3) Weigh 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate granules into a reaction vessel. Add the two lithium compounds separately into the reaction vessel. Weigh 10g of the Na synthesized in step (2). 0.69 Co 0.95 Al 0.03 Mg 0.02 O2 was poured into the reaction vessel and mixed initially, and then ion exchanged at 280℃ for 0.5 h to obtain the sample;

[0117] (4) After the crude product was washed by deionized water filtration three times, it was dried at 90℃ for 8 hours to obtain sample 1B#.

[0118] ICP was used to detect and analyze 1B#, and the specific results are shown in Table 1B.

[0119] Examples 2B-9B

[0120] The preparation methods of Examples 2B-9B are basically the same as those of Example 1B, except that different M2 sources are selected in step (1), and the mass ratio between each metal source is also selected. The specific selection is shown in Table 1B. Finally, samples 2B#-9B# are obtained, and the ICP detection and analysis results are shown in Table 1B.

[0121] Example 10B

[0122] The preparation method of Example 10B is basically the same as that of Example 1B, except that step (1) is: weighing 36.56g of sodium carbonate powder and weighing 79.30g of the aluminum-doped cobalt tetroxide compound (Co 0.95 Al 0.03 )3O4 is placed in a high-speed mixing device, the mixing program is set, and the mixture is mixed 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 is considered that the mixture is uniform after confirming that there are no white sodium carbonate spots in the mixture.

[0123] The sodium metal oxide obtained in the final step 2) is Na 0.69 Co 0.97 Al 0.03 O2 and sample 10B# is Li 0.71 Na 0.02 Co 0.97 Al 0.03 O2.

[0124] Example 11B

[0125] The preparation method of Example 11B is basically the same as that of Example 10B, except that the ion exchange time in step (3) is 1 hour. The obtained sample 11B# is Li 0.71 Na 0.02 Co 0.97 Al 0.03 O2.

[0126] Example 12B

[0127] The preparation method of Example 12B is basically the same as that of Example 10B, except that in step (3), 9.24g of lithium carbonate particles are used to replace 17.24g of lithium nitrate particles. The resulting sample 12B# is Li 0.71 Na 0.02 Co 0.97 Al 0.03 O2.

[0128] Example 13B

[0129] The preparation method of Example 13B is basically the same as that of Example 10B, except that in step (3), 10.59g of lithium chloride particles are used to replace 17.24g of lithium nitrate particles. The resulting sample 13B# is Li 0.71 Na 0.02 Co 0.97 Al 0.03 O2.

[0130] Table 1B

[0131]

[0132]

[0133] Example 1C

[0134] The positive electrode active material in this embodiment is prepared according to the following method:

[0135] (1) Weigh 36.56g of sodium carbonate powder, 1.854g of boric acid powder, and 282.32g of cobalt nitrate hexahydrate powder, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. Take out the mixture and confirm that there are no white sodium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0136] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X well-type muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 750℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample. The sodium metal oxide Na was detected by inductively coupled plasma atomic emission spectrometry (ICP). 0.69 Co 0.97 B 0.03 O2;

[0137] (3) Weigh 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate granules into a reaction vessel. Add the two lithium compounds separately into the reaction vessel. Weigh 10g of the Na synthesized in step (2). 0.69 Co 0.97 B 0.03 O2 was poured into the reaction vessel and mixed initially, then ion exchanged at 280℃ for 0.5 h to obtain the crude product;

[0138] (4) After the crude product was washed by deionized water filtration three times, it was dried at 90℃ for 8 hours to obtain sample 1C#.

[0139] ICP was used to detect and analyze 1C#, and the specific results are shown in Table 1C.

[0140] Figure 3 This is a SEM image of sample 1C# in Example 1C of the present invention.

[0141] Example 2C-9C

[0142] The preparation methods of Examples 2C-9C are basically the same as those of Example 1C. The only difference is that different M1 (B source or P source), M2 source, and mass ratio between each metal source are selected in step (1). The specific selection is shown in Table 1C. Finally, samples 2C#-9C# are obtained, and their ICP detection and analysis results are shown in Table 1C. Figure 4 This is a SEM image of sample 3C# in Example 3C of the present invention.

[0143] Example 10C

[0144] The preparation method of Example 10C is basically the same as that of Example 1C, except that step (1) is as follows: weigh 36.56g of sodium carbonate powder, weigh 1.236g of boric acid powder, and weigh 79.30g of a compound (Co) that has been doped with aluminum. 0.95 Al 0.03 )3O4 is placed in a high-speed mixing device, the mixing program is set, and the mixture is mixed 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 is considered that the mixture is uniform after confirming that there are no white sodium carbonate spots in the mixture.

[0145] The sodium metal oxide obtained in the final step 2) is Na 0.69 Co 0.95 B 0.02 Al 0.03 O2 and the 10C# sample is Li 0.71 Na 0.02 Co 0.95 B 0.02 Al 0.03 O2.

[0146] Example 11C

[0147] The preparation method of Example 11C is basically the same as that of Example 10C, except that the ion exchange time in step (3) is 1 hour. The obtained sample 11C# is Li 0.71 Na 0.02 Co 0.95 B 0.02 Al 0.03 O2.

[0148] Example 12C

[0149] The preparation method of Example 12C is basically the same as that of Example 10C, except that in step (3), 9.24g of lithium carbonate particles are used to replace 17.24g of lithium nitrate particles. The obtained sample 12C# is Li 0.71 Na 0.02 Co 0.95 B 0.02 Al 0.03 O2.

[0150] Example 13C

[0151] The preparation method of Example 13C is basically the same as that of Example 10C, except that in step (3), 10.59g of lithium chloride particles are used to replace 17.24g of lithium nitrate particles. The obtained sample 13C# is Li 0.71 Na 0.02 Co 0.95 B 0.02 Al 0.03 O2.

[0152] Table 1C

[0153]

[0154] Example 1D

[0155] The positive electrode active material in this embodiment is prepared according to the following method:

[0156] (1) Weigh 36.56g of sodium carbonate powder, 0.21g of potassium carbonate powder, 282.31g of cobalt nitrate hexahydrate powder and 1.21g of nano magnesium oxide powder, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. Take out the mixture and confirm that there are no white sodium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0157] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X well-type muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 750℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample. The sodium metal oxide Na was detected by inductively coupled plasma atomic emission spectrometry (ICP). 0.69 K 0.003 Co 0.97 Mg 0.03 O2;

[0158] (3) Weigh 10.49g of lithium hydroxide monohydrate and 17.24g of lithium nitrate granules into a reaction vessel. Add the two lithium compounds separately into the reaction vessel. Weigh 10g of the Na synthesized in step (2). 0.69 K 0.003 Co 0.97 Mg 0.03 O2 was poured into the reaction vessel and mixed initially, and then ion exchanged at 280℃ for 0.5 h to obtain the sample;

[0159] (4) After the crude product was washed by deionized water filtration three times, it was dried at 90℃ for 8 hours to obtain sample 1D#.

[0160] ICP was used to detect and analyze 1D#, and the specific results are shown in Table 1D.

[0161] Examples 2D-9D

[0162] The preparation methods of Examples 2D-9D are basically the same as those of Example 1D, except that different M2 sources are selected in step (1), and the mass ratio between each metal source is also selected. The specific selection is shown in Table 1D. Finally, samples 2D#-9D# are obtained, and their ICP detection and analysis results are shown in Table 1D.

[0163] Example 10D

[0164] The preparation method of Example 10D is basically the same as that of Example 1D, except that the ion exchange time in step (3) is 1 hour. The obtained sample 10D# is Li 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O2.

[0165] Example 11D

[0166] The preparation method of Example 11D is basically the same as that of Example 1D, except that the ion exchange temperature in step (3) is 260℃. The obtained sample 10D# is Li 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O2.

[0167] Example 12D

[0168] The preparation method of Example 12D is basically the same as that of Example 1D, except that in step (3), 9.24g of lithium carbonate particles are used to replace 17.24g of lithium nitrate particles. The obtained sample 12D# is Li 0.71 Na0.02 K 0.003 Co 0.97 Mg 0.03 O2.

[0169] Example 13D

[0170] The preparation method of Example 13D is basically the same as that of Example 1D, except that in step (3), 10.59g of lithium chloride particles are used to replace 17.24g of lithium nitrate particles. The obtained sample 13D# is Li 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O2.

[0171] Table 1D

[0172]

[0173]

[0174] Comparative Example 1

[0175] The chemical composition of the positive electrode active material in this comparative example is Li 1.0026 CoO2;

[0176] The preparation method includes the following steps:

[0177] (1) Weigh lithium carbonate and commercially available undoped spherical Co3O4 particles in a molar ratio of Li:Co = 100.26:100. Use the same stirring equipment as in the experimental example to put the two substances into a high-speed mixing device, set the mixing program, mix at 300 rpm for 3 minutes, mix at 500 rpm for 5 minutes, and then mix at 1000 rpm for 10 minutes. Take out the mixture and confirm that there are no white lithium carbonate spots in the mixture. It is considered that the mixture is uniform.

[0178] (2) Take about 30g of the well-mixed material and put it evenly into a ceramic crucible. Use a well-type muffle furnace with model VBF-1200X for high-temperature sintering. The sintering temperature rise curve is 5℃ / min. When the temperature rises to 1050℃, sinter at a constant temperature for 10h. After sintering, let it cool naturally to room temperature and then take out the sample to obtain the sintered crude product.

[0179] (3) After the crude product is crushed and ground, the powder is placed in a muffle furnace and sintered at 950°C for 8 hours. Then, the sintered product is crushed to obtain Li without any doping coating and with a D50 of 15.2 μm. 1.0026 CoO2.

[0180] Comparative Example 2

[0181] The positive electrode active material in this comparative example is a conventional high-voltage doped and coated lithium cobalt oxide positive electrode material, with a chemical composition of Li. 1.0027 Co 0.97 Al 0.03 O2.

[0182] The preparation method includes the following steps:

[0183] (1) Weigh lithium carbonate and commercially available spherical Co3O4 particles with Al doping, with a stoichiometric ratio of Co:Al = 97:3.0, using the same stirring equipment as in the experimental example. Place the two substances into a high-speed mixing device, set the mixing program, mix at 300 rpm for 3 minutes, mix at 500 rpm for 5 minutes, and then mix at 1000 rpm for 10 minutes. Take out the mixture and confirm that there are no white lithium carbonate spots in the mixture. The mixture is considered to be uniform.

[0184] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 1030℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample to obtain Li. 1.0027 Co 0.97 Al 0.03 O2.

[0185] Comparative Example 3

[0186] The preparation method of Comparative Example 3 is basically the same as that of Example 1A, except that step (1) is: weigh 36.56g of sodium carbonate powder and 291.05g of cobalt nitrate hexahydrate powder, without adding any additives, put them into a high-speed mixing device, set the mixing program, mix at 300rpm for 3 minutes, mix at 500rpm for 5 minutes, and then mix at 1000rpm for 10 minutes. After taking out the mixture, it is considered that the mixture is uniform after confirming that there are no white sodium carbonate spots in the mixture.

[0187] After processing in steps (2)-(4), the product of Comparative Example 3 with structure T2 was obtained, with the chemical formula Li. 0.71 Na 0.02 CoO2.

[0188] Comparative Example 4

[0189] The positive electrode active material in this comparative example is a conventional high-voltage doped and coated lithium cobalt oxide positive electrode material, with a chemical composition of Li. 1.0027 Co0.947 K 0.003 Mg 0.03 La 0.02 O2.

[0190] The preparation method includes the following steps:

[0191] (1) Weigh lithium carbonate, commercially available spherical Co3O4 particles doped with Mg and La, and magnesium oxide particles in a molar ratio of Li:Co:K = 100.27:94.7:0.3. The stoichiometric ratio of the Co3O4 particles is Co:Mg:La = 94.7:3.0:2. Place the three substances into a high-speed mixing device using the same stirring equipment as in the experimental example. Set the mixing program, mix at 300 rpm for 3 minutes, then mix at 500 rpm for 5 minutes, and then mix at 1000 rpm for 10 minutes. Take out the mixture and confirm that there are no white lithium carbonate spots in the mixture. The mixture is considered to be uniform.

[0192] (2) Take about 30g of the well-mixed material and evenly pack it into a ceramic crucible. Use a VBF-1200X muffle furnace for high-temperature sintering. The sintering temperature rise rate is 5℃ / min. When the temperature reaches 1030℃, sinter at a constant temperature for 10h. After sintering, allow it to cool naturally to room temperature and then remove the sample to obtain the product Li from Comparative Example 4. 1.0027 Co 0.947 K 0.003 Mg 0.03 La 0.02 O2.

[0193] Experimental Example 1

[0194] XRD diffraction was performed on the products of all embodiments and comparative examples, and the results are shown in Tables 2A to 2D.

[0195] Experimental Example 2

[0196] After fabricating the products from all the embodiments and comparative examples into positive electrode sheets, they were assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain a lithium-ion battery. The method includes:

[0197] 1) The positive electrode active materials in the examples and comparative examples were mixed with conductive carbon black and PVDF at a weight ratio of 96%:2%:2% respectively, and dispersed to obtain a positive electrode slurry. The slurry was coated onto an aluminum foil current collector and rolled to prepare a positive electrode sheet;

[0198] 2) Artificial graphite, styrene-diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black were mixed in a weight ratio of 94%:3%:2%:1%. The mixture was dispersed in water and then mixed using a double planetary mixer to obtain a negative electrode slurry. This slurry was coated onto a copper current collector, followed by rolling and drying.

[0199] Subsequently, a lithium material layer, which is a lithium foil, is deposited on the surface of the negative electrode active layer by rolling. The areal density of metallic lithium is 1.0 mg / cm³. 2 Ultimately, a negative electrode containing lithium metal is obtained.

[0200] 3) Then, the positive electrode, negative electrode and separator are assembled into a lithium-ion battery and injected with a non-aqueous electrolyte.

[0201] The electrolyte is a conventional electrolyte known in the art, which is mixed with ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) in a mass ratio of 2:5:3. Then, 5% of fluoroethylene carbonate (FEC) and 13% of lithium hexafluorophosphate (LiPF6) are added, along with the additive shown in Formula T, with the additive content accounting for 2% of the total electrolyte content.

[0202] The capacity retention rate of each lithium-ion battery was tested. The specific test method was as follows: at 25°C, the battery was charged at a constant current rate of 1C to 4.50V, then charged at a constant voltage rate of 0.05C to 4.50V, and then discharged at a discharge rate of 1C to 3.0V. This charge-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 Tables 2A to 2D.

[0203] Capacity retention rate Q = (Discharge capacity at the 500th cycle) / (Discharge capacity at the first cycle) * 100%

[0204] Figure 5 The curves show the comparison of the cycling performance of sample 1D# in Example 1D of the present invention and the sample in Comparative Example 3.

[0205] Experimental Example 3

[0206] After fabricating the products from all embodiments and comparative examples into positive electrode sheets, they were assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain a coin cell. The method includes:

[0207] The positive electrode active materials from the examples and comparative examples were mixed with conductive carbon black (SP) and PVDF in a weight ratio of 80%:10%:10% to obtain a positive electrode slurry through dispersion. This slurry was coated onto an aluminum foil current collector and rolled to prepare a positive electrode sheet. The positive electrode sheet was then punched into small discs with a diameter of 12 mm using a die-cutting tool. After drying and weighing, the discs were assembled into a coin cell using a 2025 coin cell casing, a Li metal disc as the negative electrode, and conventional high-voltage lithium cobalt oxide electrolyte in a glove box under an Ar protective atmosphere.

[0208] After each coin cell was left to stand for 4 hours under normal conditions, its initial charge-discharge capacity was tested. The test conditions were: charging at 0.1C to 4.55V, constant voltage charging to 0.025C, followed by a 3-minute rest period, and then discharging at 0.1C to 3.0V. During the discharge process, the discharge capacity C1 from 4.4 to 4.55V, the discharge capacity C2 from 3.7 to 3.8V, the total initial discharge capacity C0, and the initial charge capacity were recorded. The initial 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 Tables 2A to 2D.

[0209] Test Example 4

[0210] After assembling the products from all examples and comparative examples into lithium-ion batteries according to the method in Test Example 2, they underwent formation treatment. The lithium-ion batteries were then discharged to 3.0V at 1 / 10 of their rated capacity, and the voltage was tested, finding it to be between 3.0 and 3.6V. The lithium-ion batteries were then disassembled, and the positive electrode was removed. The positive electrode was soaked in dimethyl carbonate (DMC) for 3 hours or rinsed with DMC, then naturally dried in a drying room, and finally calcined in a muffle furnace at 300°C for 3 hours. After sieving through a 200-mesh sieve, sample powder was obtained. The content of each element in the sample powder was tested using ICP, and n was calculated based on the detected values ​​of elements such as Li and Na. The results are shown in Tables 2A-2D.

[0211] Table 2A

[0212]

[0213] Table 2B

[0214]

[0215] Table 2C

[0216]

[0217] Table 2D

[0218]

[0219] According to Tables 2A to 2D:

[0220] 1. As can be seen from Examples 1 (ABCD) to 9 (ABCD), although the selection and ratio of different M1 and M2 sources have a certain influence on the composition and crystal structure of the synthesized lithium metal oxide, compared with the comparative examples, the lithium-ion batteries in the examples have outstanding specific capacity and cycle performance under high voltage (4.5V, 4.55V and above voltage system).

[0221] It should be emphasized that although the product of Comparative Example 3 has a crystal structure that is basically the same as that of the Examples, its performance in terms of specific capacity and cycle performance is still somewhat different from that of the Examples because it does not have the doping of specific elements.

[0222] 2. According to the comparison between Example 1 (ABCD) and Examples 10-13 (ABCD), different preparation parameters such as reaction temperature, reaction time, and raw material selection have a certain impact on the composition and crystal structure of lithium metal oxide, and ultimately affect the relevant performance of lithium-ion batteries.

[0223] 3. Although Comparative Example 3 has 002 and 131 peaks, the ratio of the intensity of its 002 and 131 peaks is significantly lower because it does not have M1 dopant, so its cycling performance is not ideal.

[0224] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode and a negative electrode. The positive electrode includes a positive electrode active material, which includes a lithium metal oxide as shown in Formula 1 or Formula 2. The positive electrode active material consists of a core including the lithium metal oxide and a coating layer covering at least a portion of the surface of the core. The coating layer is selected from carbon-containing compounds and fast ion conductor materials. In the X-ray diffraction pattern, the lithium metal oxide is a cubic crystal system in space group Cmca, and has a 002 peak with a 2θ of 17.9°~18.1° and a 131 peak with a 2θ of 67.0°~67.5°. Li n1-y1 Na y1 Co 1-a1-b1 M1 b1 M2 a1 O2 Formula 1 Li n2-y2-b2 Na y2 Co 1-a2 M1 b2 M2 a2 O2 formula 2 In Equation 1, 0.6 ≤ n1 ≤ 0.8, 0 < y1 ≤ 0.05, 0 ≤ a1 ≤ 0.1, 0 < b1 ≤ 0.1, 0 <b1 / 1-a1-b1<0.1; In Equation 2, 0.6 ≤ n² ≤ 0.8, 0 < y² ≤ 0.05, 0 ≤ a² ≤ 0.1, 0 < b² ≤ 0.

02. Wherein, M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1; M1 in Formula 1 contains B atoms, wherein the insertion of B atoms replaces Co atoms in lithium metal oxide; The median particle size of the positive electrode active material is 12 μm to 20 μm; The peak intensity of the 002 peak is I1, the peak intensity of the 131 peak is I2, and I1 / I2≥4; The first-stage discharge capacity ratio of the positive electrode active material is C1 / C0≥9%, and the second-stage discharge capacity ratio is C2 / C0≥25%. Wherein, C0 is the discharge capacity of the half-cell including the positive electrode active material when it is discharged at a voltage of 3.0~4.55V; in the discharge process, the capacity released by the half-cell when it is discharged from the initial discharge voltage to 4.4V is defined as C1, and the capacity released by the half-cell when it is discharged from 3.8V to 3.7V is defined as C2.

2. The lithium-ion battery according to claim 1, characterized in that, In Equation 2, M1 is K.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, When the cutoff voltage is 3.0~3.6V and the SOC is zero, the positive electrode active material has the following properties: 0.7≤n1≤1.0 and 0.7≤n2≤1.

0.

4. The lithium-ion battery according to claim 1, characterized in that, The negative electrode is a lithium-containing negative electrode.

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