Coated and modified lithium cobalt oxide, and preparation method therefor and use thereof

Abstract

A coated and modified lithium cobalt oxide, and a preparation therefor and the use thereof. By coating the surface of lithium cobalt oxide with Na, Ni, a rare earth metal and P, the cycling performance and initial efficiency of a lithium cobalt oxide positive electrode material can be improved under a relatively high voltage of 4.2 V or higher, and the comprehensive performance of the material can be improved; moreover, Na and the rare earth metal serving as dual pillars can maintain the structural stability of the surface layer of the material, and the synergistic effect of a sodium salt coating layer and a composite coating layer is more conducive to an improvement in the cycling performance of the material.

Description

Coated modified lithium cobalt oxide and its preparation method and application Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to coated modified lithium cobalt oxide, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium cobalt oxide (LCO) dominates the 3C industry due to its compactness and high capacity density. To meet the needs of ever-increasing consumer electronics, the primary development strategy for LCO is to increase its energy density by increasing its operating voltage. However, increasing the voltage increases interfacial reactions with the electrolyte, accelerating metal dissolution and exacerbating surface cracking. This can lead to severe layered cracking in the bulk, causing a significant drop in the material's cycling performance.

[0003] Existing technologies typically employ a method of doping more Al to stabilize the bulk structure, and then coating with cobalt sources and metal compounds to improve interface stability and adapt the material to higher operating voltages. High Al doping is the primary technique for stabilizing the bulk phase. The higher the voltage, the higher the Al content in the bulk phase. Doping the bulk phase with more Al will reduce the initial efficiency of the material. The coated cobalt source and metal compound typically react with the substrate to absorb excess lithium in the substrate, forming a lithium-containing solid solution. This can mitigate electrolyte corrosion and damage to the material surface. However, the resulting lithium cobalt oxide still has limited initial efficiency and interface stability at high voltages, making it difficult to meet practical needs.

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

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide coated modified lithium cobalt oxide and its preparation method and application, so as to improve the cycle performance of lithium cobalt oxide.

[0007] The present invention is achieved in that:

[0008] In a first aspect, the present invention provides a coated modified lithium cobalt oxide, comprising a substrate and a sodium salt coating layer and a composite coating layer sequentially coated on the substrate;

[0009] The general formula of the matrix is ​​Li 1+u Co 1-v M v O, wherein 0≤u≤0.1, 0≤v≤0.1, and M is at least one of Mg, Co, Ni, Mn, Al, Ti, Ge, La, Ba, Zr, Y, V, W, Nb, Cu, B, Sr, Ga, Zn, Mo, Si, Sb, Ca, and Ta;

[0010] The general formula of the composite coating is Li 1-x Na x Co1-y-z Ni y Me z O 2-m (PO4) 2m / 3 , wherein 0<x≤0.005, 0<y≤0.01, 0<z≤0.003, 0<m≤0.001, and Me is at least one rare earth element.

[0011] In some embodiments, the thickness of the sodium salt coating layer is 10 nm to 20 nm, and the mass of the sodium salt coating layer is 0.8 wt % to 1.2 wt % of the mass of the substrate.

[0012] In some embodiments, the sodium salt in the sodium salt coating layer is at least one of sodium carbonate, sodium chloride, sodium oxalate, sodium acetate and sodium nitrate.

[0013] In some embodiments, the composite coating layer has a thickness of 20 nm to 40 nm.

[0014] In some embodiments, the average diameter of the matrix is ​​3.0 μm to 18 μm.

[0015] In some embodiments, Me is at least one of La and Y.

[0016] In a second aspect, the present invention provides a method for preparing the coated modified lithium cobalt oxide according to any one of the aforementioned embodiments, comprising:

[0017] Pre-coating: coating the substrate with sodium salt to obtain pre-coated particles having the sodium salt coating layer on the surface;

[0018] Coating: coating the pre-coated particles with the composite coating layer to obtain the coated modified lithium cobalt oxide.

[0019] In some embodiments, the pre-coating step is to spray a solution containing the sodium salt on the substrate and dry the sodium salt on the substrate until the sodium salt on the substrate surface reaches a specified thickness or mass to obtain pre-coated particles.

[0020] In some embodiments, the drying temperature is 180°C-200°C.

[0021] In some embodiments, the concentration of sodium ions in the solution containing the sodium salt is 15 wt%-25 wt%, the spraying time is 1 min-3 min, and the drying time is 0.5 h-2 h.

[0022] In some embodiments, the coating step is to mix the pre-coated particles with a gel containing a raw material of the composite coating layer, followed by calcination to obtain the coated modified lithium cobalt oxide.

[0023] In some embodiments, the gel comprises coating layer raw materials, a chelating agent and water, the concentration of the chelating agent in the gel is 0.4 wt%-0.7 wt%, and the mass ratio of the coating layer raw materials to the chelating agent is 0.25%-0.4%.

[0024] In some embodiments, the coating agent raw material includes lithium salts, sodium salts, cobalt salts, nickel salts, rare earth element compounds and phosphates.

[0025] In some embodiments, the lithium salt includes at least one of lithium carbonate, lithium acetate, and lithium hydroxide.

[0026] In some embodiments, the sodium salt in the coating agent raw material includes sodium chloride and at least one of sodium dihydrogen phosphate, sodium carbonate and sodium acetate.

[0027] In some embodiments, the cobalt salt includes at least one of cobalt sulfate and cobalt acetate, cobalt trioxide, cobalt oxyhydroxide, and cobalt hydroxide.

[0028] In some embodiments, the nickel salt includes at least one of nickel chloride, nickel nitrate, and nickel sulfate.

[0029] In some embodiments, the rare earth element compound includes at least one of an oxide of a rare earth element and a carboxylate of a rare earth element.

[0030] In some embodiments, the phosphate includes at least one of sodium dihydrogen phosphate and disodium hydrogen phosphate.

[0031] In some embodiments, the chelating agent is at least one of ammonia monohydrate, salicylic acid, and citric acid.

[0032] In some embodiments, the mass of the coating layer raw material used in the coating step is 1.2%-1.35% of the mass of the pre-coated particles.

[0033] In some embodiments, in the coating step, the calcination temperature is 550° C.-650° C., the calcination time is 5 h-7 h, and the atmosphere is an inert gas atmosphere.

[0034] In some embodiments, after the coating step, the coated modified lithium cobalt oxide is crushed to obtain coated modified lithium cobalt oxide particles.

[0035] In some embodiments, the method further includes preparing a matrix: sintering a mixture of matrix raw materials to obtain a matrix.

[0036] In some embodiments, the sintering temperature is 1000° C.-1100° C., the sintering time is 7 h-9 h, and the atmosphere is oxygen.

[0037] In a second aspect, the present invention provides an electrode comprising the coated and modified lithium cobalt oxide according to any one of the aforementioned embodiments or the coated and modified lithium cobalt oxide obtained by the method according to any one of the aforementioned embodiments.

[0038] In a third aspect, the present invention provides a battery comprising the electrode described in the aforementioned embodiment.

[0039] In a fourth aspect, the present invention provides an electrical device comprising the battery described in the aforementioned embodiment.

[0040] The present invention has the following beneficial effects:

[0041] The present invention discloses that by coating Na, Ni, rare earth metals and P on the surface of lithium cobalt oxide, the cycle and first efficiency can be improved at a higher voltage above 4.4V, thereby enhancing the comprehensive performance of the material. At the same time, Na and rare earth metals act as dual pillars to maintain the structural stability of the surface layer of the material. The sodium salt coating layer and the composite coating layer work synergistically, which is more conducive to the improvement of the cycle performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0043] FIG1 is a flow chart of Example 1;

[0044] FIG2 is a SEM image of the substrate in Example 1;

[0045] FIG3 is a SEM image of the composite coating layer in Example 1. DETAILED DESCRIPTION

[0046] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0047] The present disclosure provides a coated modified lithium cobalt oxide, comprising a substrate and a sodium salt coating layer and a composite coating layer sequentially coated on the substrate;

[0048] The general formula of the matrix is ​​Li 1+u Co 1-v M vO, wherein 0≤u≤0.1, 0≤v≤0.1, and M is at least one of Mg, Co, Ni, Mn, Al, Ti, Ge, La, Ba, Zr, Y, V, W, Nb, Cu, B, Sr, Ga, Zn, Mo, Si, Sb, Ca, and Ta;

[0049] The general formula of the composite coating is Li 1-x Na x Co 1-y-z Ni y Me z O 2-m (PO4) 2m / 3 , wherein 0<x≤0.005, 0<y≤0.01, 0<z≤0.003, 0<m≤0.001, and Me is at least one rare earth element.

[0050] The core in the present disclosure can be undoped lithium cobalt oxide. For example, when M is Co, it can also be doped modified lithium cobalt oxide. The doping element can be one of the above-mentioned M, or a combination of two, three or even more. For example, M can be a combination of Ni and Mn, a combination of V, W, Nb and Cu, or a combination of B, Sr, Ga, Zn, Mo and Si.

[0051] Na in the coating + There are three functions: 1) It can support the composite coating layer and increase the mechanical strength of the material during the charge and discharge process. + It can reduce the voltage drop and keep the ion channel open; ② During the first cycle of charge and discharge, Na + Can slow down the active Li + consumption, so there will be more active Li + Returning to the active site of the positive electrode can improve the first cycle efficiency of the material; ③Ni can produce higher capacity, but Ni 2+ Easy with Li + Mixed, sodium salt coating can slow down Ni 2+ He Li + Mixed arrangement maintains the stability of the coating layer, the gaps between the primary particles are small, and the material is not prone to crack expansion. At the same time, the Na in the coating layer + The sodium salts are derived from the composite coating and the sodium salt coating, forming a sodium salt concentration gradient within the coating. The sodium salt content is low within the coating and high outside. Furthermore, the migration rate of Na+ is lower than that of Li+. Based on the low-Na → high-Na coating, the effect on the lattice parameters is reduced, interlayer bonding is increased, and the interlayer structure of the LiCoO2 surface is stabilized. During high-voltage charge and discharge, the sodium composite coating can also compensate for charge loss, avoid phase changes caused by oxidation reactions, and maintain the stability of the material during cycling.

[0052] The main functions of Ni in the composite coating are: ①Ni doping in the Co position is conducive to the deintercalation of more active lithium from the coating layer, contributing to higher capacity; ②The valence band gap of Ni-O is wider than that of Co-O, so it can reduce the loss of lattice oxygen caused by the narrowing of the Co-O valence band gap under high voltage, maintain the stability of the surface Co-O, and reduce the loss of lattice oxygen.

[0053] Rare earth metal Me has ductility and oxygen fixation properties. The composite coating layer with Me added can reduce the mechanical stress of the material, increase the ductility of the pole piece during rolling, and reduce the cracks in the material caused by rolling. The Me-O bond is stronger than Co-O and Ni-O, and can fix surface oxygen. At the same time, Me can serve as a pillar and bind with Na + Together they stabilize the structure of the coating.

[0054] The main functions of phosphate in the composite coating: ①P-O has a stronger binding force and can stabilize the O in the coating 2- , to prevent O 2- becomes O 1- , which has a better restraining effect on the coating layer under high voltage; ② The addition of P element, the structure of the entire coating layer appears to have a composition similar to LiCoPO4, and its application voltage is above 5V, which is beneficial for the material to withstand higher voltages.

[0055] In some embodiments, the thickness of the sodium salt coating layer is 10nm-20nm, which refers to the average thickness, specifically 10nm, 12nm, 14nm, 16nm, 18nm, 20nm or any value between 10nm and 20nm, and the mass of the sodium salt coating layer is 0.8wt%-1.2wt% of the mass of the substrate, specifically 0.8wt%, 1.0wt%, 1.2wt% or any value between 0.8wt% and 1.2wt%.

[0056] In some embodiments, the sodium salt in the sodium salt coating layer is at least one of sodium carbonate, sodium chloride, sodium oxalate, sodium acetate and sodium nitrate, for example, it can be a mixture of sodium carbonate or sodium chloride and sodium oxalate.

[0057] In some embodiments, the composite coating layer has a thickness of 20 nm to 40 nm, where the thickness refers to an average thickness, and specifically can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, or any value between 20 nm and 40 nm.

[0058] In some embodiments, the average diameter of the matrix is ​​3 μm to 18 μm.

[0059] In some embodiments, Me is at least one of La and Y, for example, a combination of La or Pr and Nd.

[0060] In a second aspect, the present invention provides a method for preparing the coated modified lithium cobalt oxide according to any one of the aforementioned embodiments, comprising:

[0061] Pre-coating: coating the substrate with sodium salt to obtain pre-coated particles having the sodium salt coating layer on the surface;

[0062] Coating: coating the pre-coated particles with the composite coating layer to obtain the coated modified lithium cobalt oxide.

[0063] In some embodiments, the pre-coating step is to spray a solution containing the sodium salt on the substrate and dry the sodium salt on the substrate until the sodium salt on the substrate surface reaches a specified thickness or mass to obtain pre-coated particles.

[0064] The sodium salt coating layer is formed on the substrate surface by spraying and drying, and the coating layer is more uniform and dense. Specifically, the substrate can be placed at a drying temperature and sprayed onto the substrate at the same time, so that the sodium salt in the spray is gradually coated on the substrate surface.

[0065] In some embodiments, the drying temperature is 180°C-200°C, specifically 180°C, 185°C, 190°C, 195°C, 200°C or any value between 180°C and 200°C.

[0066] In some embodiments, the concentration of sodium ions in the solution containing the sodium salt is 15wt%-25wt%, specifically 15wt%, 17wt%, 19wt%, 21wt%, 23wt%, 25wt% or any value between 15wt% and 25wt%; the spraying time is 1min-3min, specifically 1min, 1.5min, 2min, 2.5min, 3min or any value between 1min and 3min; the drying time is 0.5h-2h, specifically 0.5h, 1h, 1.5h, 2h or any value between 0.5h and 2h.

[0067] In some embodiments, the coating step is to mix the pre-coated particles with a gel containing a raw material of the composite coating layer, followed by calcination to obtain the coated modified lithium cobalt oxide.

[0068] In this embodiment, since the surface of the pre-coated particles is sodium salt, which is water-soluble, to avoid loss of the sodium salt coating, the pre-coated particles are not directly mixed with the composite coating layer raw materials before adding water and a chelating agent to form a gel. Instead, the gel is prepared and then mixed with the pre-coated particles. Furthermore, in this embodiment, to minimize loss of the sodium salt coating, mixing with the gel should be performed as quickly as possible.

[0069] In some embodiments, the gel includes a coating layer raw material, a chelating agent and water, and the concentration of the chelating agent in the gel is 0.4wt%-0.7wt%, specifically 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt% or any value between 0.4wt% and 0.7wt%; the mass ratio of the coating layer raw material to the chelating agent is 0.25%-0.4%, specifically 0.25%, 0.3%, 0.35%, 0.4% or any value between 0.25% and 0.4%.

[0070] In some embodiments, the coating agent raw material includes lithium salt, sodium salt, cobalt salt, nickel salt, rare earth element compound and phosphate. Selecting a water-soluble coating agent raw material is more conducive to its uniform dispersion in the gel.

[0071] In some embodiments, the lithium salt includes at least one of lithium carbonate, lithium acetate, and lithium hydroxide.

[0072] In some embodiments, the sodium salt in the coating agent raw material includes sodium chloride and at least one of sodium dihydrogen phosphate, sodium carbonate and sodium acetate.

[0073] In some embodiments, the cobalt salt includes at least one of cobalt sulfate and cobalt acetate, cobalt trioxide, cobalt oxyhydroxide, and cobalt hydroxide.

[0074] In some embodiments, the nickel salt includes at least one of nickel chloride, nickel nitrate, and nickel sulfate.

[0075] In some embodiments, the rare earth element compound includes at least one of an oxide of a rare earth element and a carboxylate of a rare earth element.

[0076] In some embodiments, the phosphate includes at least one of sodium dihydrogen phosphate and disodium hydrogen phosphate.

[0077] In some embodiments, the chelating agent is at least one of ammonia monohydrate, salicylic acid, and citric acid.

[0078] In some embodiments, the mass of the coating layer raw material used in the coating step is 1.2%-1.35% of the mass of the pre-coated particles, specifically 1.2%, 1.25%, 1.3%, 1.35% or any value between 1.2% and 1.35%.

[0079] In some embodiments, in the coating step, the calcination temperature is 550°C-650°C, specifically 550°C, 570°C, 590°C, 610°C, 630°C, 650°C or any value between 550°C and 650°C; the calcination time is 5h-7h, specifically 5h, 5.5h, 6h, 6.5h, 7h or any value between 5h-7h; the atmosphere is an inert gas atmosphere, such as argon, nitrogen, etc.

[0080] In some embodiments, after the coating step, the coated modified lithium cobalt oxide is crushed to obtain coated modified lithium cobalt oxide particles.

[0081] In some embodiments, the method further includes preparing a matrix: sintering a mixture of matrix raw materials to obtain a matrix.

[0082] In some embodiments, the sintering temperature is 1000°C-1100°C, specifically 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C or any value between 1000°C-1100°C; the time is 7h-9h, specifically 7h, 7.5h, 8h, 8.5h, 9h or any value between 7h-9h; and the atmosphere is oxygen.

[0083] In a second aspect, the present invention provides an electrode comprising the coated and modified lithium cobalt oxide according to any one of the aforementioned embodiments or the coated and modified lithium cobalt oxide obtained by the method according to any one of the aforementioned embodiments.

[0084] In a third aspect, the present invention provides a battery comprising the electrode described in the aforementioned embodiment.

[0085] In a fourth aspect, the present invention provides an electrical device comprising the battery described in the aforementioned embodiment.

[0086] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0087] Example 1

[0088] This embodiment provides a method for preparing coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 Mg 0.01 O2; the sodium salt coating layer is sodium carbonate; the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O 1.85 (PO4) 0.1 , as shown in Figure 1, includes the following steps:

[0089] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide and magnesium oxide are uniformly mixed and sintered at 1070℃ for 8 hours in an oxygen atmosphere, and then the lithium cobalt oxide matrix is ​​crushed to obtain Li 1.045 Co 0.99 Mg 0.01 O2, as shown in Figure 1.

[0090] 2) preparing a sodium carbonate solution, sodium carbonate: deionized water = 2:10 (mass ratio), adding the sodium carbonate solution to a spray device, the sodium carbonate solution concentration is 20wt%, spraying it in a dynamic drying furnace equipment (the material is stirred while spraying so that the sodium carbonate solution can be relatively evenly attached to the substrate), the spraying time is 2min, and the material is dynamically dried at 190°C for 2 hours, wherein the mass of the sprayed sodium carbonate is 1wt% of the mass of the lithium cobalt oxide substrate.

[0091] 3) Lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, sodium dihydrogen phosphate, citric acid, and 5 g / L ammonia water were placed in a container and magnetically stirred at 300 rpm / min for 1 hour to prepare a gel. The lithium cobalt oxide matrix dried in step 2 was then mixed with the gel, wherein the mass ratio of the lithium cobalt oxide matrix, citric acid, and ammonia in the ammonia water was 1:0.4:3, and the total mass of the lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, and sodium dihydrogen phosphate was 1.27% of the mass of the lithium cobalt oxide matrix.

[0092] 4) Place the gel from the previous step into a muffle furnace and introduce Ar gas at a flow rate of 10 m 3 / h, sintered at 600℃ for 6 hours, and then crushed with a stone grinder to obtain a composite layer coated with lithium cobalt oxide, as shown in Figure 3. The general formula of the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O 1.85 (PO4) 0.1 .

[0093] Example 2:

[0094] This embodiment provides a method for preparing coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 La 0.01 O2; the sodium salt coating layer is sodium carbonate; the composite coating layer is Li 0.995 Na 0.005 Co 0.997 Y 0.003 O 1.85 (PO4) 0.1 , including the following steps:

[0095] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide, and lanthanum acetate were uniformly mixed and sintered at 1070 ° C for 8 hours in an oxygen atmosphere, and then the lithium cobalt oxide matrix was crushed to obtain Li 1.045 Co 0.99 La 0.01 O2.

[0096] 2) preparing a sodium carbonate solution with a mass ratio of sodium carbonate to deionized water of 2:10, adding the sodium carbonate solution to a spray device to a concentration of 20 wt %, spraying the solution in a dynamic drying furnace for 2 minutes, and performing dynamic drying at 180° C.-200° C. for less than 2 hours, wherein the mass of the sprayed sodium carbonate is 1 wt % of the mass of the lithium cobalt oxide substrate.

[0097] 3) Lithium acetate, cobalt acetate, nickel nitrate, yttrium oxide, sodium dihydrogen phosphate, citric acid, and 5 g / L ammonia water were placed in a container and magnetically stirred at 300 rpm / min for 1 hour to prepare a gel. The lithium cobalt oxide matrix dried in step 2 was then mixed with the gel, wherein the mass ratio of the lithium cobalt oxide matrix, citric acid, and ammonia in the ammonia water was 1:0.4:3, and the total mass of the lithium acetate, cobalt acetate, nickel nitrate, yttrium acetate, and sodium dihydrogen phosphate was 1.27% of the mass of the lithium cobalt oxide matrix.

[0098] 4) Place the gel in the muffle furnace and introduce Ar gas at a flow rate of 10m 3 / h, sintered at 600℃ for 6 hours, and then crushed with a stone grinder to obtain a composite layer coated with lithium cobalt oxide. The general formula of the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 Y 0.003 O 1.85 (PO4) 0.1 .

[0099] Example 3:

[0100] This embodiment provides a method for preparing coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 Zr 0.01 O2; the sodium salt coating layer is sodium carbonate; the composite coating layer is Li 0.995 Na 0.005 Co 0.997 Ce 0.003 O 1.85 (PO4) 0.1 , including the following steps:

[0101] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide and zirconium oxide are uniformly mixed and sintered at 1070℃ for 8 hours in an oxygen atmosphere, and then the lithium cobalt oxide matrix is ​​crushed to obtain Li 1.045 Co 0.99 Zr 0.01 O2.

[0102] 2) preparing a sodium carbonate solution with a mass ratio of sodium carbonate to deionized water of 2:10, adding the sodium carbonate solution to a spray device to a concentration of 20 wt %, spraying the solution in a dynamic drying furnace for 2 minutes, and performing dynamic drying at 180° C.-200° C. for less than 2 hours, wherein the mass of the sprayed sodium carbonate is 1 wt % of the mass of the lithium cobalt oxide substrate.

[0103] 3) Lithium acetate, cobalt acetate, nickel nitrate, cerium oxide, sodium dihydrogen phosphate, citric acid, and 5 g / L ammonia water were placed in a container and magnetically stirred at 300 rpm / min for 1 hour to prepare a gel. The lithium cobalt oxide matrix dried in step 2 was then mixed with the gel, wherein the mass ratio of the lithium cobalt oxide matrix, citric acid, and ammonia in the ammonia water was 1:0.4:3, and the total mass of the lithium acetate, cobalt acetate, nickel nitrate, cerium oxide, and sodium dihydrogen phosphate was 1.27% of the mass of the lithium cobalt oxide matrix.

[0104] 4) Place the gel in the muffle furnace and introduce Ar gas at a flow rate of 10m 3 / h, sintered at 600℃ for 6 hours, and then crushed with a stone grinder to obtain a composite layer coated with lithium cobalt oxide. The general formula of the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 Ce 0.003 O 1.85 (PO4) 0.1 .

[0105] Example 4

[0106] This embodiment provides a method for preparing coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 Mg 0.01 O2; the sodium salt coating layer is sodium carbonate; the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O 1.85 (PO4) 0.1 , including the following steps:

[0107] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide and magnesium oxide are uniformly mixed and sintered at 1070℃ for 8 hours in an oxygen atmosphere, and then the lithium cobalt oxide matrix is ​​crushed to obtain Li 1.045 Co 0.99 Mg 0.01 O2.

[0108] 2) preparing a sodium carbonate solution, sodium carbonate: deionized water = 2:10 (mass ratio), adding the sodium carbonate solution to a spray device, the sodium carbonate solution concentration is 20wt%, spraying in a dynamic drying furnace equipment, the spraying time is 2min, and performing dynamic drying at 180°C for 2 hours, wherein the mass of the sprayed sodium carbonate is 1.2wt% of the mass of the lithium cobalt oxide substrate.

[0109] 3) Lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, sodium dihydrogen phosphate, citric acid, and 5 g / L ammonia water were placed in a container and magnetically stirred at 300 rpm / min for 1 hour to prepare a gel. The lithium cobalt oxide matrix dried in step 2 was then mixed with the gel, wherein the mass ratio of the lithium cobalt oxide matrix, citric acid, and ammonia in the ammonia water was 1:1.4:3, and the total mass of the lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, and sodium dihydrogen phosphate was 1.2% of the mass of the lithium cobalt oxide matrix.

[0110] 4) Place the gel from the previous step into a muffle furnace and introduce Ar gas at a flow rate of 10 m 3 / h, sintered at 550℃ for 7 hours, and then crushed with a stone grinder to obtain a composite layer coated with lithium cobalt oxide. The general formula of the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O 1.85 (PO4) 0.1 .

[0111] Example 5

[0112] This embodiment provides a method for preparing coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 Mg 0.01 O2; the sodium salt coating layer is sodium carbonate; the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O 1.85 (PO4) 0.1 , as shown in Figure 1, includes the following steps:

[0113] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide and magnesium oxide are uniformly mixed and sintered at 1070℃ for 8 hours in an oxygen atmosphere, and then the lithium cobalt oxide matrix is ​​crushed to obtain Li 1.045 Co 0.99 Mg 0.01 O2.

[0114] 2) preparing a sodium carbonate solution, sodium carbonate: deionized water = 2:10 (mass ratio), adding the sodium carbonate solution to a spray device, the sodium carbonate solution concentration is 20wt%, spraying in a dynamic drying furnace equipment, the spraying time is 2min, and performing dynamic drying at 200°C for 2 hours, wherein the mass of the sprayed sodium carbonate is 0.8wt% of the mass of the lithium cobalt oxide substrate.

[0115] 3) Lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, sodium dihydrogen phosphate, citric acid, and 5 g / L ammonia water were placed in a container and magnetically stirred at 300 rpm / min for 1 hour to prepare a gel. The lithium cobalt oxide matrix dried in step 2 was then mixed with the gel, wherein the mass ratio of the lithium cobalt oxide matrix, citric acid, and ammonia in the ammonia water was 1:0.4:3, and the total mass of the lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, and sodium dihydrogen phosphate was 1.35% of the mass of the lithium cobalt oxide matrix.

[0116] 4) Place the gel from the previous step into a muffle furnace and introduce Ar gas at a flow rate of 10 m 3 / h, sintered at 650℃ for 5 hours, and then crushed with a stone grinder to obtain a composite layer coated with lithium cobalt oxide. The general formula of the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O 1.85 (PO4) 0.1 .

[0117] Comparative Example 1 (not containing sodium salt coating layer):

[0118] This comparative example provides a method for preparing a coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 Zr 0.01 O2; composite coating layer is Li1Co 0.987 Ni 0.01 Ge 0.003 O 1.85 (PO4) 0.1 , including the following steps:

[0119] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide and zirconium oxide are uniformly mixed and sintered at 1070℃ for 8 hours in an oxygen atmosphere, and then the lithium cobalt oxide matrix is ​​crushed to obtain Li 1.045 Co 0.99 Zr 0.01 O2;

[0120] 2) A lithium cobalt oxide matrix, lithium carbonate, cobalt sulfate, nickel chloride, germanium oxide, lithium phosphate, and 5 g / L ammonia solution were placed in a container, wherein the mass ratio of the matrix, citric acid, and ammonia in the ammonia solution was 1:0.4:3. The mixture was magnetically stirred at 300 rpm / min for 1 hour to obtain a gel containing the matrix, wherein the total mass of the lithium carbonate, cobalt sulfate, nickel chloride, germanium oxide, and organophosphate was 1.27% of the mass of the lithium cobalt oxide matrix.

[0121] 3) Place the gel from the previous step into a muffle furnace and introduce Ar gas at a flow rate of 10 m 3 / h, sintered at 600℃ for 6 hours, and then crushed with a stone grinder to obtain a composite layer coated with lithium cobalt oxide. The general formula of the composite coating layer is Li1Co 0.987 Ni 0.01 Ge 0.003 O 1.85 (PO4) 0.1 .

[0122] Comparative Example 2 (composite coating layer does not contain sodium ions):

[0123] This comparative example provides a method for preparing a coated modified lithium cobalt oxide, wherein the matrix of the coated modified lithium cobalt oxide is Li 1.045 Co 0.99 Y 0.01 O2; the sodium salt coating layer is sodium carbonate; the composite coating layer is LiCo 0.987 Ni 0.01 Y .003 O2, including the following steps:

[0124] 1) Preparation of lithium cobalt oxide matrix: lithium carbonate, cobalt trioxide and yttrium oxide were mixed evenly, sintered at 1070℃ for 8 hours under oxygen atmosphere, and then the lithium cobalt oxide matrix was crushed to obtain Li 1.045 Co 0.99 Y 0.01 O2.

[0125] 2) preparing a sodium carbonate solution (sodium carbonate: deionized water = 2:10 (mass ratio) and adding the sodium carbonate solution to a spray device at a concentration of 20 wt %. The solution was sprayed in a dynamic drying oven for 2 minutes and then dynamically dried at 180° C.-200° C. for 2 hours. The mass of the sprayed sodium carbonate was 1 wt % of the mass of the lithium cobalt oxide substrate.

[0126] 3) A lithium cobalt oxide matrix, lithium acetate, cobalt acetate, nickel nitrate, yttrium oxide, acetic acid, and 5 g / L ammonia water were placed in a container and magnetically stirred at a speed of 300 rpm / min for 1 hour to prepare a gel. The lithium cobalt oxide matrix dried in step 2 was then mixed with the gel, wherein the mass ratio of the lithium cobalt oxide matrix, citric acid, and ammonia in the ammonia water was 1:0.4:3, and the total mass of the lithium acetate, cobalt acetate, nickel nitrate, and yttrium oxide was 1.27% of the mass of the lithium cobalt oxide matrix.

[0127] 4) Place the gel from the previous step into a muffle furnace and introduce Ar gas at a flow rate of 10 m 3 / h, sintered at 600℃ for 6 hours, and then crushed by stone grinding to obtain a composite layer coated with lithium cobalt oxide.

[0128] Comparative Example 3:

[0129] The only difference from Example 1 is that in step (3), sodium dihydrogen phosphate is replaced by sodium carbonate, and the composite coating layer is Li 0.995 Na 0.005 Co 0.987 Ni 0.01 La 0.003 O2.

[0130] Comparative Example 4:

[0131] The only difference from Example 1 is that the gel in step (3) does not contain lanthanum acetate, and the composite coating layer is Li 0.995 Na 0.005 Co 0.99 Ni 0.01 O 1.85 (PO4) 0.1 .

[0132] Comparative Example 5:

[0133] The only difference from Example 1 is that the gel in step (3) does not contain nickel nitrate, and the composite coating layer is Li 0.995 Na 0.005 Co 0.997 La 0.003 O 1.85 (PO4) 0.1 .

[0134] Comparative Example 6:

[0135] The only difference from Example 1 is that in step (3), the lithium cobaltate matrix is ​​mixed with lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, sodium dihydrogen phosphate, citric acid and ammonia water to prepare a gel.

[0136] Comparative Example 7:

[0137] The only difference from Example 1 is that the spraying time in step (2) is 0.5 min.

[0138] Comparative Example 8:

[0139] The only difference from Example 1 is that the spraying time in step (2) is 5 minutes.

[0140] Comparative Example 9:

[0141] The only difference from Example 1 is that the mass of the sodium carbonate sprayed in step (2) is 0.5 wt % of the mass of the lithium cobalt oxide substrate.

[0142] Comparative Example 10:

[0143] The only difference from Example 1 is that the mass of the sodium carbonate sprayed in step (2) is 1.5 wt % of the mass of the lithium cobalt oxide substrate.

[0144] Comparative Example 11:

[0145] The only difference from Example 1 is that the total mass of lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, and sodium dihydrogen phosphate in step (3) is 1.6% of the mass of the lithium cobaltate matrix.

[0146] Comparative Example 12:

[0147] The only difference from Example 1 is that the total mass of lithium acetate, cobalt acetate, nickel nitrate, lanthanum acetate, and sodium dihydrogen phosphate in step (3) is 0.9% of the mass of the lithium cobaltate matrix.

[0148] Battery cell production:

[0149] The composite-coated lithium cobalt oxide positive electrode material, Super P, and PVDF were mixed in a mass ratio of 92:4:4, NMP was added, and the mixture was stirred to form a slurry. The slurry was then coated on aluminum foil and dried at 90°C to form a positive electrode sheet. The soft-pack battery was made by stacking the sheets. The discharge capacity at 25°C and the first efficiency and high-temperature cycle performance at 45°C were tested. The results are shown in Table 1.

[0150] Table 1 Capacity and cycle performance of composite-coated lithium cobalt oxide at 3.0-4.55V / 0.2C full-electric test Industrial Applicability

[0151] The present invention discloses that by coating Na, Ni, rare earth metals and P on the surface of lithium cobalt oxide, the cycle and first efficiency can be improved at a higher voltage above 4.4V, thereby enhancing the comprehensive performance of the material. At the same time, Na and rare earth metals act as dual pillars to maintain the structural stability of the surface layer of the material. The sodium salt coating layer and the composite coating layer work synergistically, which is more conducive to the improvement of the cycle performance of the material, and thus is conducive to the large-scale production and application of the material.

Claims

1. A coated modified lithium cobalt oxide, characterized in that: It comprises a substrate and a sodium salt coating layer and a composite coating layer sequentially coated on the substrate; The general formula of the matrix is ​​Li 1+u Co 1-v M v O, wherein 0≤u≤0.1, 0≤v≤0.1, and M is at least one of Mg, Co, Ni, Mn, Al, Ti, Ge, La, Ba, Zr, Y, V, W, Nb, Cu, B, Sr, Ga, Zn, Mo, Si, Sb, Ca, and Ta; The general formula of the composite coating is Li 1-x Na x Co 1-y-z Ni y Me z O 2-m (PO4) 2m / 3 , wherein 0<x≤0.005, 0<y≤0.01, 0<z≤0.003, 0<m≤0.001, and Me is at least one of the rare earth elements.

2. The coated modified lithium cobalt oxide according to claim 1, characterized in that: The thickness of the sodium salt coating layer is 10 nm-20 nm, and the mass of the sodium salt coating layer is 0.8 wt %-1.2 wt % of the mass of the substrate.

3. The coated modified lithium cobalt oxide according to claim 1 or 2, characterized in that: The sodium salt in the sodium salt coating layer is at least one of sodium carbonate, sodium chloride, sodium oxalate, sodium acetate and sodium nitrate.

4. The coated modified lithium cobalt oxide according to any one of claims 1 to 3, characterized in that: The thickness of the composite coating layer is 20nm to 40nm.

5. The coated modified lithium cobalt oxide according to any one of claims 1 to 4, characterized in that: The average diameter of the matrix is ​​3.0 μm-18 μm.

6. The coated modified lithium cobalt oxide according to any one of claims 1 to 5, characterized in that: Me is at least one of La and Y.

7. A method for preparing the coated modified lithium cobalt oxide according to any one of claims 1 to 6, characterized in that: include: Pre-coating: coating the substrate with sodium salt to obtain pre-coated particles having the sodium salt coating layer on the surface; Coating: coating the composite coating layer on the pre-coated particles to obtain the coated modified lithium cobalt oxide.

8. The method for preparing coated modified lithium cobalt oxide according to claim 7, characterized in that: The pre-coating step is to spray the solution containing the sodium salt on the substrate and dry the sodium salt on the substrate, and then continue to spray the solution containing the sodium salt and dry it until the sodium salt on the substrate surface reaches a specified thickness or mass to obtain pre-coated particles.

9. The method for preparing coated modified lithium cobalt oxide according to claim 8, characterized in that: The drying temperature is 180℃-200℃.

10. The method for preparing coated modified lithium cobalt oxide according to claim 8 or 9, characterized in that: The concentration of sodium ions in the solution containing the sodium salt is 15wt%-25wt%, the spraying time is 1min-3min, and the drying time is 0.5h-2h.

11. The method for preparing coated modified lithium cobalt oxide according to any one of claims 7 to 10, characterized in that: The coating step is to mix the pre-coated particles with the gel of the raw material containing the composite coating layer, and then calcine to obtain the coated modified lithium cobalt oxide.

12. The method for preparing coated modified lithium cobalt oxide according to claim 11, characterized in that: The gel comprises coating layer raw materials, chelating agent and water. The concentration of the chelating agent in the gel is 0.4wt%-0.7wt%, and the mass ratio of the coating layer raw materials to the chelating agent is 0.25%-0.4%.

13. The method for preparing coated modified lithium cobalt oxide according to claim 12, characterized in that: The coating agent raw materials include lithium salt, sodium salt, cobalt salt, nickel salt, rare earth element compound and phosphate.

14. The method for preparing coated modified lithium cobalt oxide according to claim 13, characterized in that: The lithium salt includes at least one of lithium carbonate, lithium acetate and lithium hydroxide.

15. The method for preparing coated modified lithium cobalt oxide according to claim 13 or 14, characterized in that: The sodium salt in the coating agent raw material includes at least one of sodium chloride and sodium dihydrogen phosphate, sodium carbonate and sodium acetate.

16. The method for preparing coated modified lithium cobalt oxide according to any one of claims 13 to 15, characterized in that: The cobalt salt includes at least one of cobalt sulfate and cobalt acetate, cobalt trioxide, cobalt oxyhydroxide and cobalt hydroxide.

17. The method for preparing coated modified lithium cobalt oxide according to any one of claims 13 to 16, characterized in that: The nickel salt includes at least one of nickel chloride, nickel nitrate and nickel sulfate.

18. The method for preparing coated modified lithium cobalt oxide according to any one of claims 13 to 17, characterized in that: The rare earth element compound includes at least one of an oxide of a rare earth element and a carboxylate of a rare earth element.

19. The method for preparing coated modified lithium cobalt oxide according to any one of claims 13 to 18, characterized in that: The phosphate includes at least one of sodium dihydrogen phosphate and disodium hydrogen phosphate.

20. The method for preparing coated modified lithium cobalt oxide according to any one of claims 13 to 19, characterized in that: The chelating agent is at least one of ammonia monohydrate, salicylic acid and citric acid.

21. The method for preparing coated modified lithium cobalt oxide according to any one of claims 11 to 20, characterized in that: The mass of the coating layer raw material used in the coating step is 1.2%-1.35% of the mass of the pre-coated particles.

22. The method for preparing coated modified lithium cobalt oxide according to any one of claims 11 to 21, characterized in that: In the coating step, the calcination temperature is 550° C.-650° C., the calcination time is 5 h-7 h, and the atmosphere is an inert gas atmosphere.

23. The method for preparing coated modified lithium cobalt oxide according to any one of claims 7 to 22, characterized in that: After the coating step, the coated modified lithium cobalt oxide is crushed to obtain coated modified lithium cobalt oxide particles.

24. The method for preparing coated modified lithium cobalt oxide according to any one of claims 7 to 23, characterized in that: The method also includes the preparation of the matrix: sintering the mixture of matrix raw materials to obtain the matrix.

25. The method for preparing coated modified lithium cobalt oxide according to claim 24, characterized in that: The sintering temperature is 1000° C.-1100° C., the sintering time is 7 h-9 h, and the atmosphere is oxygen.

26. An electrode, characterized in that: It includes the coated and modified lithium cobalt oxide according to any one of claims 1 to 6 or the coated and modified lithium cobalt oxide obtained by the method according to any one of claims 7 to 25.

27. A battery, characterized in that: Comprising the electrode as claimed in claim 26.

28. An electrical equipment, characterized in that: Comprising the battery of claim 27.

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