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 of this invention comprises matrix particles including lithium metal oxide and a graphite coating layer covering at least a portion of the surface of the matrix particles; the lithium metal oxide has the structure shown in Formula 1; 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 n‑y Na y Co 1‑a M a O2, Equation 1, where 0.6 ≤ n ≤ 0.8, 0 < y ≤ 0.05, 0 ≤ a < 0.2; and M is a doping element. The unique composition and crystal structure of this positive electrode active material help improve the battery's specific capacity and cycle performance, especially under high-voltage conditions, enabling the battery to maintain excellent performance.

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] The present invention provides a positive electrode active material, wherein the positive electrode active material is composed of matrix particles including lithium metal oxide and a graphite coating layer covering at least a portion of the surface of the matrix particles;

[0009] The lithium metal oxide has the structure shown in Formula 1;

[0010] 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°.

[0011] Li n-y Na y Co 1-a M a O2 Formula 1

[0012] In Equation 1, 0.6≤n≤0.8, 0<y≤0.05, 0≤a≤0.2;

[0013] Where M is a dopant element.

[0014] The positive electrode active material as described above, wherein the lithium metal oxide has the structure shown in Formula 2;

[0015] Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O2 Formula 2

[0016] In Equation 2, 0 < a1 ≤ 0.1, 0 ≤ a2 ≤ 0.1, and a1 + a2 = a;

[0017] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1.

[0018] In the positive electrode active material described above, the mass percentage W of the graphite coating layer satisfies the following condition based on the weight of the positive electrode active material: 0 < W ≤ 1%.

[0019] In the above-described positive electrode active material, the graphite coating layer is a reduced graphene oxide coating layer.

[0020] The positive electrode active material as described above, wherein, in the Raman spectrum, the lithium metal oxide at a wavelength of 1560±30 cm⁻¹ -1 Peak intensity I around G With lithium metal oxide at a wavelength of 1360±30cm -1 The peak intensity on the left and right is I D Satisfy: I D / I G ≥68%.

[0021] 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 ≤ n ≤ 1.0.

[0022] 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.

[0023] The present invention provides a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode active material as described above.

[0024] The positive electrode as described above includes a current collector, a safety layer, and a positive electrode active layer.

[0025] The safety layer is sandwiched between the current collector and the positive electrode active layer, and the positive electrode active layer includes the positive electrode active material.

[0026] The present invention provides a lithium-ion battery, wherein the lithium-ion battery includes a positive electrode as described above.

[0027] The lithium-ion battery described above, wherein the negative electrode in the lithium-ion battery is a lithium-containing negative electrode.

[0028] 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

[0029] Figure 1 This is a schematic diagram of the structure of an embodiment of the negative electrode sheet in the lithium-ion battery of the present invention;

[0030] Figure 2 This is a SEM image of the positive electrode active material in Example 1 of the present invention;

[0031] Figure 3 These are Raman spectroscopy results of the positive electrode active materials in Examples 1 and 9 of this invention.

[0032] Figure 4 This is the XRD pattern of the positive electrode active material in Example 8 of the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 20: Negative electrode active layer;

[0035] 30: Lithium material layer;

[0036] 101: Negative electrode current collector. Detailed Implementation

[0037] 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.

[0038] The first aspect of the present invention provides a positive electrode active material, which is composed of matrix particles including lithium metal oxide and a graphite coating layer covering at least a portion of the surface of the matrix particles;

[0039] Lithium metal oxides have the structure shown in Formula 1;

[0040] 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°.

[0041] Li n-y Na y Co 1-a M a O2 Formula 1

[0042] In Equation 1, 0.6≤n≤0.8, 0<y≤0.05, 0≤a≤0.2;

[0043] Where M is a dopant element.

[0044] It is understood that the graphite coating layer can cover part of the surface of the matrix particles or the entire surface of the aggregate particles. This invention does not specifically limit the graphite coating layer; for example, the graphite coating layer can be a graphene coating layer and / or a reduced graphene oxide coating layer.

[0045] The lithium metal oxide described above in this invention specifically includes oxides of at least lithium, cobalt, and sodium. Furthermore, it may be doped with M. This invention does not limit the specific selection of M and it can be a common doping element in the art. For example, it can be at least one of the elements W, Mg, Ti, Mn, Al, Te, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B, and P.

[0046] This invention does not impose excessive restrictions on y and a within the above-mentioned limits.

[0047] For example, in Equation 1, y 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; a 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.

[0048] It is important to emphasize that the above limitation of n refers 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.

[0049] According to the above-described solution provided by the present invention, compared with other positive electrode active materials, the specific capacity and cycle performance of lithium-ion batteries are significantly improved after applying the positive electrode active material including the lithium metal oxide to lithium-ion batteries, and the electrical performance of lithium-ion batteries will not deteriorate even under high voltage operating conditions.

[0050] Based on this phenomenon, the inventors analyzed it and believe it may be due to the following: On the one hand, by setting a graphite coating layer, the positive electrode active material has a core-shell structure consisting of a lithium metal oxide core and a graphite coating layer covering the core. This coating layer helps to reduce or suppress side reactions between the lithium metal oxide and the electrolyte. Even when the battery is operating under high voltage, a stable interface can still be formed between the positive electrode active material and the electrolyte. This improves the battery's cycle performance by preventing excessive dissolution of metal ions from the positive electrode active material and avoiding electrolyte shortage. At the same time, the suppression or reduction of side reactions also... This reduces the amount of gas generated inside the battery, thus ensuring its safety performance. On the other hand, the graphite coating itself has good electron transport properties, which allows the positive electrode active material, including the graphite coating, to further improve the conductivity of the positive electrode active material, thereby increasing the charge and discharge capacity of the lithium-ion battery. At the same time, the lithium metal oxide with the above-mentioned crystal characteristics has a more complete layered crystal phase structure, which reduces or suppresses the occurrence of internal mixing phenomena, thereby enabling lithium ions to be smoothly inserted and extracted, especially exhibiting multiple small charge and discharge plateaus during high-voltage charge and discharge processes.

[0051] Furthermore, the inventors discovered that by classifying the doping elements in lithium metal oxides, the performance of the cathode active material can be further improved. In some embodiments of the present invention, the lithium metal oxide has the structure shown in Formula 2;

[0052] Li n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O2 Formula 2

[0053] In Equation 2, 0 < a1 ≤ 0.1, 0 ≤ a2 ≤ 0.1, and a1 + a2 = a;

[0054] M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1.

[0055] It is understood that the lithium metal oxide of the present invention may also have the structure shown in Formula 2, specifically including at least an oxide of lithium, cobalt, sodium, and M1. Furthermore, it may be doped with M2, which is different from M1. The present invention does not limit the specific selection of M2, and it can be a doping element commonly used in the art. For example, it can be at least one of the elements Mg, Ti, Mn, Al, Te, Ni, Nb, Zr, La, F, Ce, Sr, Y, K, B, and P.

[0056] This invention does not impose excessive restrictions on a1 and a2 within the above-mentioned scope.

[0057] For example, in Equation 2, a1 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; 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, 0.020, 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.

[0058] In this invention, the application of the lithium metal oxide positive electrode active material, including Formula 2, to lithium-ion batteries can further improve the specific capacity and cycle performance of lithium-ion batteries, enabling them to operate at high voltage for a longer period without degradation. Based on this phenomenon, the inventors believe that the doping of M1 helps to support the structure of the lithium metal oxide, thereby improving its structural stability to a certain extent. Therefore, regardless of whether the operating environment is at normal or high voltage, a structurally stable lithium metal oxide is more conducive to improving the efficiency of lithium-ion insertion / extraction, thus promoting the improvement of the cycle performance and specific capacity of lithium-ion batteries.

[0059] In this invention, the mass percentage of the graphite coating in the positive electrode active material can be further selected to maximize the advantages of both the graphite coating and lithium metal oxide, thereby improving the performance of the positive electrode active material. In some embodiments of this invention, based on the total mass of the positive electrode active material, the mass percentage W of the graphite coating satisfies: 0 < W ≤ 1%.

[0060] In some embodiments of the present invention, when the graphite coating layer is a reduced graphene oxide coating layer, the positive electrode active material exhibits superior performance. Lithium-ion batteries prepared with positive electrode active materials including reduced graphene oxide coating layers demonstrate superior specific capacity and cycle performance. This is because reduced graphene oxide has a two-dimensional crystal structure, which provides superior conductivity. When applied to positive electrode active materials, it further improves the specific capacity of the battery. Furthermore, the two-dimensional crystal structure increases the contact area between the positive electrode active material and the electrolyte, allowing for a more complete reaction between the electrolyte and the positive electrode active material, effectively reducing side reactions between the positive electrode active material and the electrolyte, and improving the battery's capacity and cycle performance.

[0061] In this invention, reduced graphene oxide refers to defective graphene obtained by reducing graphene oxide. Furthermore, this invention can also maximize the function of the reduced graphene oxide layer and improve battery capacity and cycle performance by controlling the degree of reduction of the reduced graphene oxide in the reduced graphene oxide layer. The degree of reduction of the reduced graphene oxide can be determined by observing the characteristic peaks of lithium metal oxide in the Raman spectrum.

[0062] In some embodiments of the present invention, lithium metal oxide is observed in Raman spectra at wavelengths of 1560 ± 30 cm⁻¹. -1 Peak intensity I G With lithium metal oxide at a wavelength of 1360±30cm -1 The peak intensity on the left and right is I D Satisfy: I D / I G ≥68%.

[0063] The positive electrode active material of the present invention, comprising a reduced graphene oxide coating, has a Raman spectrum with a wavelength range of 1000–2000 cm⁻¹. -1 Within the range, and including areas located at 1560cm -1 The nearby G-band, and located at 1360cm -1 The peak intensity I of the characteristic peaks in the nearby D and G bands G Peak intensity I of the characteristic peak of the D band D Satisfy: I D / I G ≥68%. This is understandable, when I... D / IG At ≥68%, reduced graphene oxide exhibits better reduction, and the positive electrode active material containing this reduced graphene oxide layer demonstrates superior performance. Furthermore, 80% ≤ I D / I G ≤90%.

[0064] As mentioned earlier, in lithium metal oxides without any charge / discharge treatment, n is 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, the n of the lithium metal oxide is between 0.7 and 1.0. It should be noted that the change in n refers to the number of charge / discharge cycles within 10. Specifically, after the aforementioned lithium metal oxides are used in charge / discharge applications, their composition changes, especially the molar amount of lithium ions increases significantly. This is because lithium metal oxides with the aforementioned crystal structure have some vacancies. Therefore, when they are used in charge / discharge applications, 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.

[0065] 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.

[0066] Furthermore, the median particle size of the positive electrode active material of the present invention is 12–20 μm, for example, 13 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.

[0067] The inventors discovered that when lithium in lithium metal oxide is more uniformly distributed within the crystal structure, multiple discharge plateaus during the charging and discharging process exhibit superior discharge capacity.

[0068] 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 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 discharged by the half-cell when discharged from 3.8V to 3.7V is defined as C2.

[0069] 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.

[0070] 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.

[0071] 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 a method including the following steps: 1) mixing the sodium metal oxide shown in Formula 1a with a lithium compound and performing ion treatment to obtain matrix particles; 2) performing a coating reaction between the matrix particles and graphite material to obtain the lithium metal oxide of the present invention.

[0072] Na x Co 1-a M a O2 Formula 1a

[0073] In Equation 1a, 0.68 < x < 0.74, 0 <a≤0.2。

[0074] The aforementioned ion exchange treatment is a thermal treatment process, specifically referring to the heat treatment of a mixture of sodium metal oxide and lithium compound at 80℃ to 300℃ for no more than 10 hours. After the ion exchange treatment, the system is washed and dried to finally obtain lithium metal oxide. The drying temperature is 80℃ to 180℃, and the time is at least 10 hours. There are no limitations on the equipment used for ion exchange treatment and drying. For example, the ion exchange treatment equipment can be a closed container with sealing and stirring capabilities, such as a wet coating reaction device or a co-precipitation reaction device; the drying equipment can be a forced-air drying oven, a vacuum drying oven, a rotary kiln, a disc dryer, or an oven.

[0075] The lithium compound mentioned above can be a commonly used lithium source compound 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 process, the mass ratio of the lithium compound to the sodium metal oxide is not less than 1:1, preferably (1-3):1.

[0076] For the sodium metal compound shown in Formula 1a, by way of example, it can be prepared by a method including the following process:

[0077] The cobalt source and the sodium source are mixed in at least the target ratio and then calcined to obtain the sodium metal compound shown in Formula 1a.

[0078] Specifically, the calcination temperature is 700–900℃, and the time is 8–50 hours. The calcination can be carried out in an oxygen or air atmosphere. The equipment used for calcination can be high-temperature sintering equipment such as muffle furnaces, tunnel furnaces, roller kilns, and tube furnaces.

[0079] The mixing of the various sources mentioned above can be performed using high-speed mixing equipment, sand milling equipment, ball milling equipment, plow milling equipment, inclined milling equipment, etc. It should be noted that if sand milling or 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 process is completed. Generally, the mixing time should not exceed 4 hours.

[0080] Preferably, the lithium metal oxide of the present invention can also be prepared by a method comprising the following steps: 1) mixing the sodium metal oxide shown in Formula 2a with a lithium compound and subjecting it to ion treatment to obtain matrix particles; 2) subjecting the matrix particles and graphite material to a coating reaction to obtain the lithium metal oxide of the present invention. The method of mixing the sodium metal oxide shown in Formula 2a with a lithium compound and subjecting it to ion treatment is used to prepare the lithium metal oxide.

[0081] Na x Co 1-a1-a2 M1 a1 M2 a2O2 Formula 2a

[0082] In Equation 2, 0 < a1 ≤ 0.1, 0 ≤ a2 ≤ 0.1, and a1 + a2 = a.

[0083] The M1 source, M2 source, cobalt source, and sodium source can be mixed in a target ratio and then calcined to obtain the sodium metal compound shown in Formula 2a.

[0084] 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, for example, an oxide containing 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, potassium carbonate, potassium nitrate, potassium hydroxide, potassium bicarbonate, potassium sulfate, etc., one or more of them; the source of M2 can be any compound containing M2, such as oxides containing M2, such as basic magnesium carbonate, magnesium hydroxide, zirconium oxide, yttrium oxide, lanthanum oxide, lanthanum fluoride, nickel oxide, niobium oxide, etc., one or more of them.

[0085] A second aspect of the present invention provides a positive electrode sheet comprising the positive electrode active material described in the first aspect above.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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).

[0090] 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.

[0091] 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.

[0092] According to the present invention, the lithium-ion battery further includes a negative electrode, a separator, and an electrolyte.

[0093] 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.

[0094]

[0095] For example, the negative electrode can be a lithium metal-rich 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.

[0096] 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.

[0097] For example, the diaphragm is a polypropylene-based material, or a coated diaphragm with ceramic coating on one or both sides.

[0098] 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).

[0099] 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.

[0100] The technical solution of the present invention will be further explained and described below with reference to specific embodiments.

[0101] Example 1

[0102] The positive electrode active material in this embodiment is prepared according to the following method:

[0103] (1) Weigh 36.56g of sodium carbonate powder and 291.05g 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.

[0104] (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 CoO2;

[0105] (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 CoO2 was poured into a reaction vessel and initially mixed, then subjected to ion exchange at 280°C for 0.5 h to obtain the crude product;

[0106] (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#.

[0107] ICP was used to detect and analyze 1B#, and the specific results are shown in Table 1;

[0108] (5) Weigh 5g of sample 1A# powder obtained in step (4) and 25mg of graphene oxide (GO). Put sample 1A# powder and graphene oxide into a beaker container, add 15ml of deionized water, and carry out the coating reaction with mechanical stirring at 45℃ for 30min. Then heat it to 65℃ until the water in the beaker container is basically evaporated. Then further reduce and dry it under vacuum at 100℃. Take out the sample to obtain sample 1A#.

[0109] The 1A# sample was tested using Raman spectroscopy, and the test results are shown in Table 2.

[0110] Figure 2 This is a SEM image of the positive electrode active material in Example 1 of the present invention. Figure 2 As can be seen, the cathode material particles of the present invention have sheet-like defective graphene layers and matrix particles, with the defective graphene layers attached to the surface of the matrix particles.

[0111] Example 2

[0112] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step (5), 35 mg of graphene oxide is weighed.

[0113] Example 3

[0114] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step (5), 15 mg of graphene oxide is weighed.

[0115] Example 4

[0116] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that the coating reaction time in step (5) is 60 min.

[0117] Example 5

[0118] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0119] Step (1) is as follows: Take 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.

[0120] The sodium metal oxide obtained in step (2) is Na 0.69 K 0.003 Co 0.97 Mg 0.03 O2;

[0121] After processing in step (4), sample 5B#Li was obtained. 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O2;

[0122] After processing in step (5), sample 5A#rGO / Li was obtained. 0.71 Na 0.02 K 0.003 Co 0.97 Mg 0.03 O2.

[0123] Example 6

[0124] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0125] Step (1) is as follows: Take 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.

[0126] The sodium metal oxide obtained in step (2) is Na 0.69 Co 0.95 Al 0.03 Mg 0.02 O2;

[0127] After processing in step (4), sample 6B#Li was obtained.0.71 Na 0.02 Co 0.95 Al 0.03 Mg 0.02 O2;

[0128] After processing in step (5), sample 6A#rGO / Li was obtained. 0.71 Na 0.02 Co 0.95 Al 0.03 Mg 0.02 O2.

[0129] Example 7

[0130] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0131] Step (1) is as follows: Take 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. Then it is considered that the mixture is uniform.

[0132] The sodium metal oxide obtained in step (2) is Na 0.69 Co 0.97 B 0.03 O2;

[0133] After processing in step (4), sample 7B#Li was obtained. 0.71 Na 0.02 Co 0.97 B 0.03 O2;

[0134] After processing in step (5), sample 7A#rGO / Li was obtained. 0.71 Na 0.02 Co 0.97 B 0.03 O2.

[0135] Example 8

[0136] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that:

[0137] Step (1) is as follows: Take 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.

[0138] The sodium metal oxide obtained in step (2) is Na 0.69 Co 0.97 Te 0.03 O2;

[0139] After processing in step (4), sample 8B#Li was obtained. 0.71 Na 0.02 Co 0.97 Te 0.03 O2;

[0140] After processing in step (5), sample 8A#rGO / Li was obtained. 0.71 Na 0.02 Co 0.97 Te 0.03 O2.

[0141] Example 9

[0142] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step (5):

[0143] The coating reaction was carried out at 25°C with mechanical stirring for 10 minutes to obtain sample 9A#.

[0144] Example 10

[0145] The preparation method of the positive electrode active material in this embodiment is basically the same as that in Example 1, except that in step (5):

[0146] Weigh out 75 mg of graphene oxide (GO), and the coating reaction time is 10 min to obtain 10A#;

[0147] Comparative Example 1

[0148] 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.

[0149] The preparation method includes the following steps:

[0150] (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.

[0151] (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.

[0152] Comparative Example 2

[0153] The preparation method of the positive electrode active material in this comparative example is basically the same as that in Example 5, except that the treatment in step (5) is not performed, and the 5A# sample obtained in step (4) is used directly as the positive electrode active material.

[0154] Experimental Example 1

[0155] XRD diffraction and Raman spectroscopy were performed on all the products of the examples and comparative examples, and the results are shown in Table 2.

[0156] Figure 3 These are Raman spectral images of the positive electrode active materials used in Examples 1 and 9 of this invention. Figure 3 It can be seen that in Example 1, I D / I G It is 80.20%, in Example 9, I D / I G It is 65.38%.

[0157] Figure 4 This is the XRD pattern of the positive electrode active material in Example 8 of the present invention. From... Figure 4 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.

[0158] Experimental Example 2

[0159] 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:

[0160] 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;

[0161] 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.

[0162] 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.

[0163] 3) Then, the positive electrode, negative electrode and separator are assembled into a lithium-ion battery and injected with a non-aqueous electrolyte.

[0164] 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.

[0165] 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 Table 2.

[0166] Capacity retention rate Q = (Discharge capacity at the 500th cycle) / (Discharge capacity at the first cycle) * 100%

[0167] Experimental Example 3

[0168] 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:

[0169] 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.

[0170] 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, then standing for 3 minutes, followed by 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 Table 2.

[0171] Table 1

[0172]

[0173]

[0174] Table 2

[0175]

[0176] According to Tables 1 and 2:

[0177] 1. According to the examples and comparative examples, different preparation parameters, such as reaction temperature, reaction time, and differences in raw material selection, have a certain impact on the composition and crystal structure of lithium metal oxides, and ultimately affect the relevant performance of lithium-ion batteries.

[0178] 2. As can be seen from Table 2, Example 5 and Comparative Example 2, the positive electrode active material prepared in the embodiments of the present invention has better specific capacity and cycle performance when applied to lithium-ion batteries, indicating that the use of redox graphene-coated matrix material to prepare positive electrode active material in the present invention can improve the electrochemical performance of positive electrode active material.

[0179] 3. As can be seen from Examples 1-4, the content of graphite coating has a slight effect on the crystal form of the positive electrode active material, which is manifested in a slight change in the position of the characteristic peak, but this effect can be ignored.

[0180] 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 positive electrode plate, characterized in that, The positive electrode includes a current collector, a safety layer, and a positive electrode active layer. The safety layer is sandwiched between the current collector and the positive electrode active layer. The positive electrode active layer includes a positive electrode active material, which is composed of matrix particles comprising lithium metal oxide and a reduced graphene oxide coating layer covering at least a portion of the surface of the matrix particles. In the Raman spectrum, the positive electrode active material is at a wavelength of 1560±30 cm⁻¹. -1 The peak intensity IG, and the positive electrode active material at a wavelength of 1360±30cm -1 The peak intensity of ID satisfies: 80% ≤ ID / IG ≤ 90%; The lithium metal oxide has the structure shown in Formula 2; 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 n-y Na y Co 1-a1-a2 M1 a1 M2 a2 O2 type 2 In Equation 2, 0.6≤n≤0.8, 0<y≤0.05, 0<a1≤0.1, 0≤a2≤0.1, 0<a1 / 1-a2<0.1; Wherein, M1 is selected from at least one of Te, W, Al, B, P and K; M2 is a doping element different from M1; Based on the total mass of the positive electrode active material, the mass percentage W of the reduced graphene oxide coating layer satisfies: 0 < W ≤ 1%; When the cutoff voltage is 3.0~3.6V and the SOC is zero, the positive electrode active material has a particle size distribution of 0.7≤n≤1.

0. The median particle size of the positive electrode active material is 12 μm to 20 μm.

2. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 1.

3. The lithium-ion battery according to claim 2, characterized in that, The negative electrode in the lithium-ion battery is a lithium-containing negative electrode.

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