Coated modified positive electrode material, preparation method thereof, positive plate and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a coated modified positive electrode material, a preparation method thereof, a positive plate and a lithium ion battery. The coated and modified positive electrode material comprises an O < 3->-LCO base material and an O < 2->-LCO coating layer; the chemical formula of the O3-LCO base material is Li1 + yCo1-xAxO2, x is greater than 0 and smaller than or equal to 0.5, y is greater than or equal to 0 and smaller than or equal to 0.2, A comprises at least one of Ni, Mn, Al, Mg, Ti, Zr, Y, La, V, Ce, Na, Cu, Fe, Zn, W, Se, Ca, Pd, Ta, Bi, P, Ba, Nb, Mo, Sb, Sn and B, and B is greater than or equal to 0 and smaller than or equal to 0.2. The chemical formula of the O2-LCO coating layer is LiqCoNapO2, q is more than or equal to 0.75 and less than or equal to 1, and p is more than 0 and less than or equal to 0.15. And the O2-LCO coating layer is arranged, so that the structural stability and the electrochemical performance of the positive electrode material under high voltage can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and more particularly to a coated and modified cathode material, a preparation method thereof, a cathode sheet, and a lithium-ion battery. Background Art

[0002] The O3-type lithium cobalt oxide (abbreviated as O3-LCO) cathode material is the preferred cathode material in the field of portable electronic products due to its ultra-high tap density and volumetric energy density.

[0003] However, the actual capacity of the currently commercial O3-LiCoO2 (about 170 mAh / g at 4.45 V) is significantly lower than its theoretical capacity (274 mAh / g), and it cannot meet the market demand for high-energy-density lithium-ion batteries. Increasing the working voltage is an effective strategy to promote LiCoO2 to obtain a higher energy density. However, at high voltages, O3-LCO faces irreversible harmful phase transitions and severe surface side reactions, which directly damage the structural stability of it, resulting in problems such as low capacity and poor cycling performance.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a coated and modified cathode material. By providing an O2-LCO coating layer on the surface of the O3-LCO matrix material, the structural stability of the cathode material at high voltages can be improved, and the electrochemical performance of the cathode material can be significantly improved. It solves the problems such as low capacity and poor cycling performance caused by the instability of the structure and interface of O3-LCO at high voltages.

[0006] The second object of the present invention is to provide a preparation method of a coated and modified cathode material. An O2-LCO coating layer is in-situ synthesized on the O3-LCO matrix material. The obtained O2-LCO coating layer is uniform and dense, and can improve the structural stability of the cathode material at high voltages and improve the electrochemical performance of the cathode material.

[0007] The third object of the present invention is to provide a cathode sheet with high capacity, high initial Coulomb efficiency, and good cycling performance.

[0008] The fourth object of the present invention is to provide a lithium-ion battery with high capacity, high initial Coulomb efficiency, and long cycle life.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] The present invention first provides a coated and modified cathode material, which includes an O3-LCO matrix material and an O2-LCO coating layer coated on the surface of the O3-LCO matrix material; wherein, the chemical formula of the O3-LCO matrix material is Li 1+y Co 1-x A x O2, where 0 < x ≤ 0.5, 0 ≤ y ≤ 0.2, and A includes at least one of the elements Ni, Mn, Al, Mg, Ti, Zr, Y, La, V, Ce, Na, Cu, Fe, Zn, W, Se, Ca, Pd, Ta, Bi, P, Ba, Nb, Mo, Sb, Sn, and B; the chemical formula of the O2-LCO coating layer is Li q CoNa p O2, where 0.75 ≤ q ≤ 1, 0 < p ≤ 0.15.

[0011] Furthermore, the O2-LCO coating layer is in-situ synthesized.

[0012] Furthermore, the volume average particle size D of the cathode material 50 is 2.5 - 22 μm.

[0013] Furthermore, the thickness of the O2-LCO coating layer is 0.5 - 15 nm.

[0014] The present invention further provides a preparation method of the above-mentioned coated and modified cathode material, including the following steps: (a) Mix the O3-LCO matrix material, sodium source, and cobalt source and then calcine to obtain an intermediate material with P2-Na z CoO2 coating O3-LCO; where 0.6 ≤ z ≤ 0.85; (b) Perform an ion exchange reaction by the liquid method or the molten salt method to convert the P2-Na z CoO2 in the intermediate material into O2-Li q CoNa p O2 to obtain the coated and modified cathode material.

[0015] Furthermore, in step (a), the sodium source includes at least one of sodium carbonate, sodium hydroxide, and sodium bicarbonate.

[0016] Furthermore, in step (a), the cobalt source includes at least one of cobalt tetroxide and cobalt hydroxide.

[0017] Furthermore, in step (a), the molar ratio of sodium element in the sodium source to cobalt element in the cobalt source is (0.6 - 0.85):1.

[0018] Furthermore, in step (a), the P2-Na in the intermediate material zThe mass ratio of CoO2 to O3-LCO is 0.1% to 10%.

[0019] Further, in step (a), the calcination temperature is 600 to 850 °C, and the holding time of the calcination is 8 to 20 h.

[0020] Further, in step (b), the steps of performing the ion replacement reaction by the liquid method include: mixing the intermediate material, the lithium source and water, and heating for ion replacement.

[0021] Further, the heating temperature is 60 to 90 °C, and the heating time is 6 to 12 h.

[0022] Further, the lithium source and the water are first mixed to form a lithium source solution with a molar concentration of 2 mol / L to 5 mol / L, and then the intermediate material is added thereto and mixed evenly.

[0023] Further, in step (b), the steps of performing the ion replacement reaction by the molten salt method include: mixing the intermediate material and the lithium source and sintering.

[0024] Further, the sintering temperature is 200 to 300 °C, and the holding time of the sintering is 1 to 5 h.

[0025] Further, the lithium source includes at least one of lithium hydroxide, lithium nitrate and lithium chloride.

[0026] Further, the molar ratio of lithium element in the lithium source to Na element in the intermediate material is (5 to 10):1.

[0027] The present invention further provides a positive electrode sheet, including the above-mentioned coated and modified positive electrode material.

[0028] The present invention further provides a lithium ion battery, including the above-mentioned positive electrode sheet.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] (1) For the coated and modified positive electrode material provided by the present invention, by coating an O2-LCO coating layer on the outer surface of the O3-LCO matrix material, the structural stability of the positive electrode material at high voltage can be improved, and the electrochemical properties such as specific capacity, initial efficiency and cycle retention rate of the positive electrode material can be improved.

[0031] (2) For the preparation method of the coated and modified positive electrode material provided by the present invention, the obtained O2-LCO coating layer is uniform and dense, and the structural stability at high voltage is significantly improved, and the electrochemical properties are significantly improved. Description of the Drawings

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 XRD comparison diagram of the positive electrode materials prepared in Example 1 and Comparative Example 1 provided by the present invention;

[0034] Figure 2 SEM diagram of the coated and modified positive electrode material prepared in Example 1 provided by the present invention;

[0035] Figure 3 SEM diagram of the coated and modified positive electrode material prepared in Example 6 provided by the present invention;

[0036] Figure 4 SEM diagram of the coated and modified positive electrode material prepared in Comparative Example 1 provided by the present invention;

[0037] Figure 5 Capacity test comparison diagram of the coin cells assembled with the positive electrode materials of Example 1 and Comparative Example 1 provided by the present invention;

[0038] Figure 6 Cycle test comparison diagram of the coin cells assembled with the positive electrode materials of Example 1 and Comparative Example 1 provided by the present invention. Specific Embodiments

[0039] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Those not specified in the embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0040] Unless otherwise specified, in the present invention, "first aspect", "second aspect", "third aspect", "fourth aspect", etc. are for descriptive purposes only, and should not be construed as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. are only for non-exhaustive listing and description purposes, and should be understood not to constitute a closed limitation on quantity.

[0041] Unless otherwise specified, "including" and "comprising" mentioned in the present invention mean open-ended, and can also be closed-ended. For example, the said "including" and "comprising" can mean that other components not listed can also be included or comprised, or only the components listed can be included or comprised.

[0042] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or more.

[0043] In a first aspect, the present invention provides a cathode material for O2-LCO-coated modified O3-LCO, the cathode material comprising an O3-LCO matrix material and an O2-LCO coating layer coated on the outer surface of the O3-LCO matrix material.

[0044] It can be understood that the O3-LCO matrix material is an O3-type lithium cobalt oxide cathode material, specifically a doped (metal or non-metal) lithium cobalt oxide material.

[0045] It can be understood that the O2-LCO coating layer is an O2-type lithium cobalt oxide material, specifically a lithium cobalt oxide material doped with Na.

[0046] Among them, O2-type LiCoO2 (abbreviated as O2-LCO) exhibits more reversible structural changes under high voltage and has more excellent cycle stability.

[0047] The chemical formula of the O3-LCO matrix material is Li 1+y Co 1-x A x O2.

[0048] Among them, 0 < x ≤ 0.5, including but not limited to any point value of 0.01, 0.03, 0.05, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or the range value between any two of them.

[0049] Among them, 0 ≤ y ≤ 0.2, including but not limited to the point values of any one of 0, 0.01, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2 or the range values between any two of them.

[0050] Among them, A includes at least one of the elements Ni, Mn, Al, Mg, Ti, Zr, Y, La, V, Ce, Na, Cu, Fe, Zn, W, Se, Ca, Pd, Ta, Bi, P, Ba, Nb, Mo, Sb, Sn and B; for example, one, two, three, four, five or more of them can be selected. A ions are introduced by bulk doping to replace Li in the lattice + or Co 3+ , which can stabilize the lattice structure, inhibit irreversible phase transformation, improve the stability of the O3-LCO matrix material structure during cycling, and improve its cycling performance and rate performance.

[0051] The chemical formula of the O2-LCO coating layer is Li q CoNa p O2. Among them, 0.75 ≤ q ≤ 1, including but not limited to the point values of any one of 0.75, 0.77, 0.78, 0.80, 0.83, 0.85, 0.88, 0.90, 0.93, 0.95, 0.98, 1 or the range values between any two of them; 0 < p ≤ 0.15, including but not limited to the point values of any one of 0.01, 0.03, 0.05, 0.08, 0.1, 0.13, 0.15 or the range values between any two of them.

[0052] The coated and modified cathode material provided by the present invention can solve the problems of low capacity and poor cycling performance caused by unstable structure and interface of O3-LCO at high voltages by coating an O2-LCO coating layer on the outer surface of the O3-LCO matrix material. The coated and modified cathode material has excellent stability and electrochemical performance at high voltages. Among them, the synergistic effect between the O2-phase LCO and the O3-phase LCO is as follows: (1) Structural compatibility: Both O3-LCO and O2-LCO belong to the layered structure, and there is a certain similarity and correlation in their crystal structures. The coating of O2-LCO on the surface of O3-LCO enables the coating layer to be well combined with the matrix, without problems such as excessive lattice mismatch. (2) Suppressing particle cracking: During the charge and discharge process of O3-LCO, due to the deintercalation and intercalation of lithium ions, phenomena such as interlayer slip and particle cracking are likely to occur. And there is a special LiO4 configuration in the T2 phase formed during the phase change of O2-LCO, which can improve the stability of the layered structure. After coating with O2-LCO, the cracking of O3-LCO particles can be effectively suppressed, and the integrity of the material structure can be maintained. (3) Improving cycling stability: The cycling stability of O2-LCO itself at high voltages is much better than that of O3-LCO. After coating O2-LCO on the surface of O3-LCO, the O2-LCO coating layer can alleviate the structural changes of O3-LCO during the charge and discharge process to a certain extent, reduce the occurrence of irreversible phase changes, and thus improve the cycling stability of the overall material. (4) Optimizing interface compatibility: The presence of O2-LCO can act as a buffer layer to improve the interface compatibility between O3-LCO and the electrolyte, and reduce the occurrence of interfacial side reactions.

[0053] Specifically, the coated and modified cathode material provided by the present invention has the advantages of high capacity, high initial Coulomb efficiency (hereinafter referred to as initial efficiency), and good cycling performance.

[0054] If O3-LCO and O2-LCO are blended as the cathode material (non-coated), they exist separately between particles and have no synergistic effect, and there is no improvement or protection effect on O3-LCO particles. However, in the present invention, by setting an O2-LCO coating layer, the O2-LCO coating can inhibit the cracking of O3-LCO particles, alleviate the volume change, optimize the interface, reduce side reactions, help form a stable interface film (CEI), and is beneficial to the transmission of lithium ions at the interface.

[0055] In some specific embodiments, the O2-LCO coating layer is in-situ synthesized. In-situ synthesizing the O2-LCO coating layer on the O3-LCO matrix material can improve the uniformity and compactness of the O2-LCO coating layer. A dense and uniform coating layer can well inhibit interfacial side reactions, stabilize the material structure, and improve the electrochemical performance. In addition, in-situ synthesis has the advantages of simple method, fast speed, and easy operation.

[0056] In some specific embodiments, the volume-average particle size D of the positive electrode material 50 is 2.5 to 22 μm; including but not limited to the point values of any one of 2.5 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, 22 μm or the range values between any two of them. When the average particle size D50 of the lithium cobalt oxide positive electrode material is within the above range, the particle strength of the lithium cobalt oxide positive electrode material is better. When the average particle size D50 of the lithium cobalt oxide positive electrode material is lower than the above range, the tap density of the lithium cobalt oxide positive electrode material may decrease; when the average particle size D50 of the lithium cobalt oxide positive electrode material is higher than the above range, the particles of the lithium cobalt oxide positive electrode material are prone to cracking.

[0057] In some specific embodiments, the thickness of the O2-LCO coating layer is 0.5 to 15 nm, including but not limited to the point values of any one of 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 13 nm, 15 nm or the range values between any two of them. When the thickness of the O2-LCO coating layer is within the above range, it can better promote the intercalation and deintercalation of lithium ions during charge and discharge, and hinder the contact between the matrix and the electrolyte, reducing side reactions.

[0058] In a second aspect, the present invention provides a method for preparing the coated and modified positive electrode material, comprising the following steps:

[0059] (a) First, mix the O3-LCO matrix material, sodium source and cobalt source evenly and then calcine, and obtain an intermediate material of P2-Na z CoO2 coating O3-LCO after cooling. That is, the P2-Na z CoO2 in the intermediate material is the coating layer. In P2-Na z CoO2, 0.6 ≤ z ≤ 0.85, including but not limited to the point values of any one of 0.6, 0.63, 0.65, 0.68, 0.70, 0.72, 0.75, 0.78, 0.80, 0.83, 0.85 or the range values between any two of them.

[0060] (b) Then, carry out an ion exchange reaction by a liquid method or a molten salt method to make the P2-Na z CoO2 coating layer in the intermediate material react and transform into an O2-Li q CoNa p O2 coating layer, and the final coated and modified positive electrode material is obtained after the reaction is completed.

[0061] In the present invention, an O2-LCO coating layer is in-situ synthesized on an O3-LCO matrix material. The preparation method is simple and environmentally friendly. The obtained O2-LCO coating layer is uniform and dense, and its structural stability at high voltages is significantly improved, and the electrochemical performance is obviously improved.

[0062] Among them, the present invention uses a liquid method or a molten salt method to carry out an ion exchange reaction, and a uniform and dense coating layer can be prepared.

[0063] In some specific embodiments, in step (a), the sodium source includes at least one of sodium carbonate, sodium hydroxide, and sodium bicarbonate.

[0064] In some specific embodiments, in step (a), the cobalt source includes at least one of cobalt tetroxide and cobalt hydroxide.

[0065] In some specific embodiments, in step (a), the volume average particle size D of the cobalt source 50 is 1-5 μm, preferably 1-2 μm. This is beneficial to better form the coating layer. If the particle size is too large, separate O2-LCO particles may be synthesized instead of the coating layer.

[0066] In some specific embodiments, in step (a), the molar ratio of sodium element in the sodium source to cobalt element in the cobalt source is (0.6-0.85):1, such as 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1 or 0.85:1; preferably (0.65-0.8):1.

[0067] In some specific embodiments, in step (a), the mass ratio of P2-Na z CoO2 in the intermediate material to O3-LCO is 0.1%-10%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 10%; preferably 3%-8%. This ratio is closely related to the subsequently synthesized O2-LCO coating layer. P2-Na z CoO2 at this ratio results in a relatively dense and uniform coating layer of O2-LCO in the later stage, which can better improve the performance.

[0068] In some specific embodiments, in step (a), the calcination temperature is 600-850 °C, including but not limited to any point value of 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C or the range value between any two of them; the calcination holding time is 8-20 h, including but not limited to any point value of 8 h, 10 h, 12 h, 15 h, 18 h, 20 h or the range value between any two of them.

[0069] In some specific embodiments, in step (b), the steps of performing the ion exchange reaction by the liquid method include: mixing the intermediate material, a lithium source, and water, heating for ion exchange, separating the solid and liquid after the reaction is completed, then washing and drying at 80-150 °C for 1-4 h to obtain the final cathode material.

[0070] In some specific embodiments, during the process of performing the ion exchange reaction by the liquid method, the heating temperature is 60-90 °C, including but not limited to any point value among 60 °C, 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C or the range value between any two of them; the heating time is 6-12 h, including but not limited to any point value among 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h or the range value between any two of them.

[0071] In some specific embodiments, during the process of performing the ion exchange reaction by the liquid method, first mix the lithium source and the water to make a lithium source solution with a molar concentration of 2 mol / L-5 mol / L, and then add the intermediate material thereto and mix evenly.

[0072] In some specific embodiments, in step (b), the steps of performing the ion exchange reaction by the molten salt method include: mixing the intermediate material and the lithium source and sintering, cooling and then dispersing and washing in deionized water, and then drying at 80-150 °C for 1-4 h to obtain the final cathode material.

[0073] In some specific embodiments, during the process of performing the ion exchange reaction by the molten salt method, the sintering temperature is 200-300 °C, including but not limited to any point value among 200 °C, 220 °C, 230 °C, 250 °C, 280 °C, 300 °C or the range value between any two of them; the heat preservation time for sintering is 1-5 h, including but not limited to any point value among 1 h, 2 h, 3 h, 4 h, 5 h or the range value between any two of them.

[0074] In some specific embodiments, during the process of performing the ion exchange reaction by the liquid method and the molten salt method, the lithium source used includes at least one of lithium hydroxide, lithium nitrate, and lithium chloride.

[0075] In some specific embodiments, during the process of ion replacement reaction using the liquid method and the molten salt method, the molar ratio of lithium element in the lithium source to Na element in the intermediate material is (5 - 10):1, including but not limited to any point value among 5:1, 6:1, 7:1, 8:1, 9:1, 10:1 or the range value between any two of them. When the lithium source includes two or three of lithium hydroxide, lithium nitrate and lithium chloride, as long as the molar ratio of all lithium elements in the lithium source to Na element in the intermediate material is (5 - 10):1, it is acceptable.

[0076] In some specific embodiments, the preparation method of the O3-LCO matrix material includes: weighing appropriate lithium-containing compounds, cobalt-containing compounds and A-containing compounds according to the molar ratio of Li element to Co element of (1.04 - 1.08):1, mixing them evenly, performing high-temperature roasting in a box furnace, and then pulverizing to obtain the O3-LCO matrix material. Among them, the cobalt-containing compound includes at least one of cobalt tetroxide, cobalt hydroxide, cobalt carbonate and cobalt oxyhydroxide, preferably cobalt tetroxide. When the cobalt-containing compound is in large particles, its volume average particle size D 50 ranges from 10 to 20 μm, preferably 14 to 18 μm. When the cobalt-containing compound is in small particles, its volume average particle size D 50 ranges from 2 to 6 μm, preferably 3 to 5 μm. The lithium-containing compound includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium acetate and lithium oxalate, preferably lithium carbonate or lithium hydroxide. The A-containing compound includes the oxide, carbonate, hydroxide, oxalate or fluoride of A, preferably the oxide or hydroxide; where A includes at least one of the elements Ni, Mn, Al, Mg, Ti, Zr, Y, La, V, Ce, Na, Cu, Fe, Zn, W, Se, Ca, Pd, Ta, Bi, P, Ba, Nb, Mo, Sb, Sn and B. The mass of the A-containing compound accounts for 0.03% - 2.0% of the mass of the cobalt-containing compound. The roasting temperature is 900 - 1100 °C, and the roasting holding time is 6 - 12 h.

[0077] In the third aspect, the present invention provides a positive electrode sheet including the coated and modified positive electrode material.

[0078] This positive electrode sheet has a high capacity, a high initial Coulomb efficiency and good cycling performance.

[0079] In some specific embodiments, the positive electrode sheet may further include a binder and a conductive agent, which are not limited in the present invention.

[0080] In the fourth aspect, the present invention provides a lithium-ion battery including the positive electrode sheet.

[0081] This lithium-ion battery has a high capacity, a high initial Coulomb efficiency and a long cycling life.

[0082] In some specific embodiments, the lithium-ion battery further includes a negative electrode sheet, a separator, and an electrolyte, which are not limited in the present invention.

[0083] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are followed. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchases.

[0084] Example 1

[0085] The preparation method of the coated and modified cathode material provided in this example includes the following steps:

[0086] (1) Weigh Li2CO3 and Co3O4 according to the molar ratio of Li element to Co element of 1.07:1, and also weigh Al2O3 and MgO, where the mass of Al2O3 is 0.3% of the mass of Co3O4, and the mass of MgO is 0.2% of the mass of Co3O4. After mixing all the raw materials evenly, put them into an air furnace, keep them at 1070 °C for 9 h, cool and then crush to obtain the O3-LCO matrix material, whose chemical formula is Li 1.041 Co 0.911 Al 0.048 Mg 0.041 O2, and its volume average particle size D 50 is 18 μm.

[0087] (2) Weigh the O3-LCO matrix material obtained in step (1), and according to the molar ratio of Na element to Co element of 0.7:1 and the weight of the finally synthesized target P2-Na 0.7 CoO2 coating layer is 5% of the weight of the O3-LCO matrix material, weigh sodium carbonate and Co(OH)2. After mixing all the raw materials evenly, put them into an air furnace, calcine at 800 °C for 10 h, and obtain the intermediate material of P2-Na 0.7 CoO2 coated on O3-LCO (i.e., z = 0.7).

[0088] (3) Using the liquid method, weigh the intermediate material obtained in step (2), and weigh LiOH according to the molar ratio of Li element to Na element in the intermediate material of 5:1. Mix LiOH and deionized water to make a 3.0 mol / L lithium source solution, and heat it to 80 °C. Then add the intermediate material into the lithium source solution and stir for ion exchange. After reacting for 10 h, rinse and dry at 120 °C for 2 h. During the reaction process, Na + in the coating layer is + replaced by Li0.85 CoNa 0.1 O2-coated O3-Li 1.041 Co 0.911 Al 0.048 Mg 0.041 The cathode material of O2, with a volume average particle size D 50 being 19 μm, O2-Li 0.85 CoNa 0.1 The thickness of the O2 coating layer is 8 nm.

[0089] Perform material phase analysis on the finally prepared coated and modified cathode material in Example 1, and the results are as Figure 1 shown; from Figure 1 it can be seen that for the cathode material after O2-LCO coated on O3-LCO, the diffraction peak results show the presence of O2-phase LCO, but no other impurity phases appear.

[0090] At room temperature, perform electron scanning on the finally prepared coated and modified cathode material in Example 1, and the results are as Figure 2 shown. From Figure 2 it can be seen that the surface of the cathode material particles prepared in Example 1 has an obvious coating layer, and the coating layer is uniform and dense.

[0091] Example 2

[0092] The preparation method of the coated and modified cathode material provided in this example is basically the same as that in Example 1, except that: in step (1), Li2CO3 and Co3O4 are weighed according to the molar ratio of Li element to Co element of 1.06:1, and Al2O3, Y2O3 and TiO2 are also weighed, where the mass of Al2O3 is 0.5% of the mass of Co3O4, the mass of Y2O3 is 0.1% of the mass of Co3O4, and the mass of TiO2 is 0.05% of the mass of Co3O4. After mixing the raw materials evenly, put them into an air furnace, keep them at 1060 °C for 10 h, cool and then crush to obtain the O3-LCO matrix material, whose chemical formula is Li 1.0064 Co 0.9063 Al 0.08 Y 0.0073 Ti 0.0064 O2, with a volume average particle size D 50 being 18 μm.

[0093] Example 3

[0094] The preparation method of the coated and modified cathode material provided in this example is basically the same as that in Example 1, except that: in step (2), according to the final synthesis target P2-Na 0.65The weight of the CoO2 coating layer is 7% of the weight of the O3-LCO matrix material. NaOH and Co(OH)2 are weighed, and after mixing the raw materials evenly, they are put into an air furnace and calcined at 750 °C for 15 h to obtain the intermediate material of P2-Na 0.65 The intermediate material with CoO2 coating O3-LCO (i.e., z = 0.65).

[0095] The O2-LCO (O2-Li 0.83 CoNa 0.1 O2) coating layer finally obtained in this example has a thickness of 11 nm.

[0096] Example 4

[0097] The preparation method of the coated and modified cathode material provided in this example is basically the same as that in Example 1, except that in step (3), LiCl is weighed according to the molar ratio of Li element to Na element in the intermediate material being 7.5:1, LiCl is dissolved in water to obtain a 5 mol / L lithium source solution, and the heating temperature is replaced with 90 °C, and the stirring reaction time is replaced with 12 h, and the chemical formula of the O2-LCO coating layer obtained is Li 0.9 CoNa 0.05 O2.

[0098] Example 5

[0099] The preparation method of the coated and modified cathode material provided in this example is basically the same as that in Example 1, except that in step (1), Li2CO3 and Co3O4 are weighed according to the molar ratio of Li element to Co element being 1.055:1, and kept at 1000 °C for 10 h, and after cooling, it is crushed to obtain the O3-LCO matrix material with the chemical formula of Li 1.041 Co 0.911 Al 0.048 Mg 0.041 O2, and its volume average particle size D 50 is 5 μm.

[0100] Example 6

[0101] Weigh the O3-LCO matrix material (volume average particle size D 50 is 18 μm) obtained in step (1) of Example 1 and the O3-LCO matrix material (volume average particle size D 50 is 5 μm) obtained in step (1) of Example 5 according to the weight ratio of 8:2, and mix them evenly. Then, the cathode material with O2-LCO coating O3-LCO is prepared according to steps (2) and (3) of Example 1.

[0102] The volume average particle size D 50 of the finally prepared cathode material in this Example 6 is 17 μm.

[0103] The scanning electron microscope of the cathode material finally obtained in this Example 6 is as Figure 3 shown. It can be seen that both the large particles and the small particles have a uniform and obvious coating layer on their surfaces.

[0104] Example 7

[0105] The preparation method of the coated and modified cathode material provided in this example is basically the same as that of Example 1, except that: step (3) is different. In this example, the molten salt method is used, and step (3) is as follows: Weigh LiNO3 and LiCl according to the molar ratio of Li element to Na element in the intermediate material being 7.5:1, where the molar ratio of LiNO3 and LiCl is 7:3. After mixing the raw materials evenly, place them in a box furnace and sinter at 250 °C for 1 h to carry out an ion exchange reaction. After cooling, disperse them evenly in deionized water, wash and dry them. Finally, obtain the O2-Li 0.85 CoNa 0.05 O2-coated O3-LCO cathode material.

[0106] Comparative Example 1

[0107] The preparation method of the cathode material provided in this comparative example includes the following steps: Weigh Li2CO3 and Co3O4 according to the molar ratio of Li element to Co element being 1.07:1. After mixing them evenly, put them into an air furnace, keep them at 1070 °C for 9 h, and after cooling, crush them to obtain the O3-LCO cathode material, whose chemical formula is LiCoO2, and its volume average particle size D 50 is 18 μm.

[0108] The scanning electron microscope of the cathode material obtained in this Comparative Example 1 is as Figure 4 shown. It can be Figure 4 seen that the surface of the lithium cobaltate cathode material particles prepared in Comparative Example 1 is smooth and clear, and there is no coating layer.

[0109] Comparative Example 2

[0110] The preparation method of the cathode material provided in this comparative example is basically the same as that of Example 1, except that: step (3) is not carried out.

[0111] That is, the cathode material of this comparative example is P2-Na 0.7 CoO2-coated O3-LCO cathode material (that is, the coating layer is P2-Na 0.7 CoO2).

[0112] Comparative Example 3

[0113] The cathode material provided in this comparative example is the Li 1.041 Co 0.911 Al 0.048 Mg 0.041O2.

[0114] Comparative Example 4

[0115] The cathode material provided in this comparative example is a mixed material (uncoated) of O2-Li 0.85 CoNa 0.1 O2 (with the Li 1.041 Co 0.911 Al 0.048 Mg 0.041 O2 (volume average particle size D 50 being 18 μm) in a weight ratio of 2:8, where the preparation method of O2-Li 0.85 CoNa 0.1 O2 is as follows: Mix Co3O4 and sodium carbonate according to a molar ratio of Na / Co = 0.7, and then sinter at 800 °C for 20 h to prepare Na 0.7 CoO2. Then, according to a molar ratio of Li / Na = 7.5, mix Na 0.7 CoO2 with LiNO3 and LiCl (the molar ratio of LiNO3 and LiCl is 7:3), and then sinter at 200 °C for 2 h to obtain O2-Li 0.85 CoNa 0.1 O2, whose volume average particle size D 50 is 5 μm.

[0116] Perform SEM tests on the cathode materials of Example 1, Example 6, and Comparative Example 1 respectively. At room temperature, use a JSM-IT100 model scanning electron microscope to test and analyze the surface morphology of the prepared cathode materials. The test results are shown in Figure 2 , Figure 3 and Figure 4 .

[0117] Perform XRD tests on the cathode materials of Example 1 and Comparative Example 1. Use a SmartLabSE model X-ray diffractometer from Japan to test and analyze the phase of the prepared cathode materials under room temperature operating conditions. The test results are shown in Figure 1 .

[0118] Experimental Example

[0119] Respectively use the cathode materials prepared in each example and each comparative example as the cathode active materials, and make button cells according to the following method: Disperse the cathode active material, conductive carbon black SP, and binder PVDF in a weight ratio of 90:5:5 into the solvent NMP and mix evenly to obtain the cathode slurry; coat the cathode slurry evenly on the cathode current collector aluminum foil, and after drying and cold pressing, obtain the cathode electrode sheet. Assemble the cathode sheet, polypropylene separator, graphite anode sheet, and electrolyte (LiPF6 propylene carbonate solution) into a button cell.

[0120] The capacity test and cycle test were respectively carried out on each button cell according to the following method: (1) Capacity test: Each button cell was tested using a blue electrochemical workstation. The test regime at room temperature was as follows: Constant current charging was carried out at a current density of 0.1C until 4.60V, followed by constant voltage charging until 50uA, and then discharging at 0.1C until 3V to test the discharge capacity. (2) Cycle test: The cycle test regime was as follows. At 45°C, with a charge-discharge rate of 1C, charge and discharge were carried out 50 times within the voltage range of 3.0V to 4.6V. The test results are shown in Table 1 below.

[0121] Among them, Figure 5 Figure 1 is a comparative chart of the capacity test of button cells assembled with the cathode materials of Example 1 and Comparative Example 1; Figure 6 Figure 2 is a comparative chart of the cycle test of button cells assembled with the cathode materials of Example 1 and Comparative Example 1.

[0122] In addition, the volume average particle size D of the cathode materials prepared in each example and each comparative example 50 and the thickness of the O2-LCO coating layer are shown in Table 1.

[0123] Table 1 Capacity and cycle test results of each battery

[0124]

[0125]

[0126] It can be seen from the data in Table 1 that compared with Comparative Examples 1-4, the cathode materials of O2-LCO coated O3-LCO prepared in Examples 1-7 have higher specific capacity, initial efficiency and cycle retention rate at high voltages. This indicates that the capacity, initial efficiency and cycle stability of the O3-LCO material at high voltages are significantly improved after being coated and modified with O2-LCO.

[0127] It can be seen that by setting an O2-LCO coating layer with a specific chemical formula on the surface of the O3-LCO matrix material and doping A in the O3-LCO matrix material, the present invention can improve the structural stability of the cathode material at high voltages and increase the specific capacity, initial efficiency and cycle retention rate of the cathode material.

[0128] Although the present invention has been illustrated and described with reference to specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; those of ordinary skill in the art should understand that: without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements 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; therefore, this means that all such replacements and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A coated modified positive electrode material, characterized in that: The positive electrode material includes an O3-LCO matrix material and an O2-LCO coating layer coated on the surface of the O3-LCO matrix material; Wherein, the chemical formula of the O3-LCO matrix material is Li 1+y Co 1-x A x O2, wherein 0<x≤0.5, 0≤y≤0.2, A includes at least one of Ni, Mn, Al, Mg, Ti, Zr, Y, La, V, Ce, Na, Cu, Fe, Zn, W, Se, Ca, Pd, Ta, Bi, P, Ba, Nb, Mo, Sb, Sn and B; The chemical formula of the O2-LCO coating is Li q CoNa p O2, where 0.75≤q≤1, 0<p≤0.

15.

2. The coated modified positive electrode material according to claim 1, characterized in that: The O2-LCO coating layer is synthesized in situ.

3. The coated modified positive electrode material according to claim 1, characterized in that: The volume average particle size D of the positive electrode material 50 2.5~22μm; And / or, the thickness of the O2-LCO coating layer is 0.5 to 15 nm.

4. The method for preparing the coated modified positive electrode material according to any one of claims 1 to 3, characterized in that: The steps include: (a) The O3-LCO matrix material, the sodium source and the cobalt source are mixed and calcined to obtain P2-Na z CoO2 coated O3-LCO intermediate material; wherein 0.6≤z≤0.85; (b) using a liquid method or a molten salt method to carry out an ion replacement reaction so that the P2-Na z CoO2 to O2-Li q CoNa p O2, to obtain the coated modified positive electrode material.

5. The method for preparing the coated modified positive electrode material according to claim 4, characterized in that: At least one of the following conditions is met: (1) In step (a), the sodium source comprises at least one of sodium carbonate, sodium hydroxide and sodium bicarbonate; (2) In step (a), the cobalt source comprises at least one of cobalt tetroxide and cobalt hydroxide; (3) In step (a), the molar ratio of the sodium element in the sodium source to the cobalt element in the cobalt source is (0.6-0.85):1; (4) In step (a), the P2-Na z The mass ratio of CoO2 to O3-LCO is 0.1% to 10%; (5) In step (a), the calcination temperature is 600-850° C., and the calcination holding time is 8-20 h.

6. The method for preparing the coated modified positive electrode material according to claim 4, characterized in that: In step (b), the step of using the liquid method to carry out ion replacement reaction includes: mixing the intermediate material, lithium source and water and heating them to carry out ion replacement; Preferably, the heating temperature is 60 to 90° C., and the heating time is 6 to 12 hours; Preferably, the lithium source and the water are first mixed to prepare a lithium source solution with a molar concentration of 2 mol / L to 5 mol / L, and then the intermediate material is added thereto and mixed evenly.

7. The method for preparing the coated modified positive electrode material according to claim 4, characterized in that: In step (b), the step of using the molten salt method to carry out the ion replacement reaction includes: mixing the intermediate material with a lithium source and sintering; Preferably, the sintering temperature is 200-300° C., and the sintering holding time is 1-5 hours.

8. The method for preparing the coated modified positive electrode material according to claim 6 or 7, characterized in that: The lithium source includes at least one of lithium hydroxide, lithium nitrate and lithium chloride; And / or, the molar ratio of the lithium element in the lithium source to the Na element in the intermediate material is (5-10):

1.

9. A positive electrode sheet, characterized in that: The invention comprises the coated and modified positive electrode material as claimed in any one of claims 1 to 3.

10. A lithium ion battery, characterized in that Comprising the positive electrode sheet as claimed in claim 9.

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