Moisture-resistant positive electrode material, and preparation method therefor and use thereof

Abstract

The present application belongs to the technical field of lithium-ion batteries. Disclosed are a moisture-resistant positive electrode material, and a preparation method therefor and the use thereof. The moisture-resistant positive electrode material provided in the present application is of a core-shell structure, and sequentially comprises an inner core material, an inner coating layer and an outer coating layer, wherein the general chemical formula of the inner core material is Li1+aNixCoyMnzMaO2, the general chemical formula of the inner coating layer is LibCoLfO2, and the outer coating layer comprises R. The material provided in the present application has good moisture resistance and electrochemical performance, and can be widely applied to the preparation of batteries.

Description

A moisture-resistant positive electrode material and its preparation method and application Technical Field

[0001] The present application belongs to the technical field of lithium-ion batteries, and in particular relates to a moisture-resistant positive electrode material and a preparation method and application thereof. Background Art

[0002] Under the background of the country advocating the concept of green and low-carbon development, the new energy industry has developed rapidly. As one of the core parts of lithium-ion batteries, cathode materials account for more than 40% of the cost of lithium batteries. x Co y Mn 1-x-y O2, 0<x, y<1) has the advantages of high energy density, good safety performance, and low cost, and is one of the main types of positive electrode materials for power lithium batteries. With technological advancements and social needs, the actual operating conditions of battery cells are becoming increasingly demanding, and the performance requirements for positive electrode materials are becoming increasingly stringent. For anhydrous lithium battery systems, a humid environment causes the material surface to react with moisture in the air, producing excessive residual lithium on the surface and causing local phase changes. This leads to reduced specific capacity, poor cycling performance, gas production, and deterioration in storage. Therefore, moisture resistance is a challenge that requires long-term research.

[0003] Most of the research on moisture-resistant applications focuses on coating with hydrophobic groups of organic matter, but this often results in high costs and reduced electrochemical activity of the materials. Therefore, research on moisture-resistant positive electrode materials is urgent.

[0004] Summary of the Invention

[0005] The purpose of this application is to overcome the deficiencies of the above-mentioned prior art and to provide a moisture-resistant positive electrode material with excellent moisture resistance and electrochemical properties, as well as a preparation method and application thereof.

[0006] To achieve the above purpose, the technical solution adopted by the present application is: a moisture-resistant positive electrode material, the moisture-resistant positive electrode material is a core-shell structure, which includes a core material, an inner coating layer and an outer coating layer in sequence; the chemical formula of the core material is Li 1+a Ni x Co y Mn z M a O2, the chemical formula of the inner coating layer is Li b CoL f O2, the outer coating layer includes R;

[0007] Among them, 0.50≤x≤0.98, 0.01≤y≤0.2, 0.01≤z≤0.49, 0 <a≤0.1,x+y+z=1;

[0008] 0 <b≤1.3,0<f≤0.4,0<A≤0.04,0<c≤0.02,0.5<b / (1+f)<0.99;

[0009] M is at least one selected from the group consisting of Na, K, Mg, Al, Ti, Zr, Sr, Y, Ce, W, La, Sn, Mo, Fe, B, and Si;

[0010] L is at least one selected from Al, Ti, W, B, Nb, Sb, F, Sn, Ce, and Mg;

[0011] R is selected from at least one of La2O3, MoO3, WO3, TiO2, Nb2O5, B2O3, and Al2O3.

[0012] The present application provides a moisture-resistant positive electrode material, comprising a core material, an inner coating layer and an outer coating layer of a specific substance, which can achieve good moisture resistance and electrochemical performance of the product; specifically, after being placed in an environment with a humidity of 40% for two days, the moisture content in the material is below 0.0576%, the residual lithium content is below 0.1782%, the volume change after high-temperature storage is below 25%, and the gram capacity retention rate after high-temperature storage is above 80%.

[0013] In one embodiment, the moisture-resistant positive electrode material satisfies at least one of the following conditions:

[0014] (a) The core material is a hexagonal layered structure with a space group of (R-3m);

[0015] (b) the inner coating layer has a spinel structure;

[0016] (c) The outer coating layer is a nanocomposite oxide layer.

[0017] Specifically, the core material is a hexagonal layered structured doped Li 1+a Ni x Co y Mn z M a O2, the hexagonal layered structure is stable and can provide good structural stability for moisture-resistant positive electrode materials; the inner coating layer is lithium-deficient Li b CoL f O2, a spinel structure, can provide surface Ni for moisture-resistant positive electrode materials. 3+ Low proportion and low oxygen defect; the outer coating layer includes R, which is a nanocomposite oxide layer with oxygen vacancy active sites, which can reduce Li + Reacting with hydroxyl groups, the moisture-resistant outer shell layer is provided to the moisture-resistant positive electrode material; that is, the present invention can achieve good moisture resistance and structural stability by selecting specific chemical substances and forming a specific layered structure, thereby ensuring good electrochemical performance.

[0018] In one embodiment, the molar ratio of the inner coating layer to the inner core is ≤0.045.

[0019] In one embodiment, the molar ratio of the inner coating layer to the inner core is 0.01-0.038.

[0020] In one embodiment, the molar ratio of R in the outer coating layer to the inner core is ≤0.02.

[0021] In one embodiment, the molar ratio of R in the outer coating layer to the inner core is 0.005-0.02.

[0022] The inventors have found that when the molar ratio of the inner coating layer to the core material is ≤0.045 and the molar ratio of R in the outer coating layer to the core material is ≤0.02, the thickness of the inner and outer coating layers can be made moderate, thereby avoiding adverse effects on the electrochemical performance; especially when the molar ratio of the inner coating layer to the core material is 0.01-0.038 and the molar ratio of R in the outer coating layer to the core material is 0.005-0.02, the comprehensive performance of the obtained product is even better; if the molar ratio of the inner coating layer to the core material is greater than 0.04 or the molar ratio of R in the outer coating layer to the core material is greater than 0.02, the capacity of the prepared product will be low, thereby reducing the electrochemical performance.

[0023] In one embodiment, M is selected from at least one of Na, Al, Zr, and Y; L is selected from at least one of Al, Ti, Sn, and Ce; and R is selected from at least one of WO3, TiO2, Nb2O5, and Al2O3.

[0024] The inventors have found that, on the one hand, when M is selected from at least one of Na, Al, Zr, and Y, the hexagonal layered structure of the core can be better stabilized; on the other hand, when L is selected from at least one of Al, Ti, Sn, and Ce, the inner coating layer can better provide surface Ni for the moisture-resistant positive electrode material. 3+ On the other hand, when R is selected from at least one of WO3, TiO2, Nb2O5, and Al2O3, it can provide more oxygen vacancy active sites, thereby reducing Li + Reacts with hydroxyl groups; the above three aspects work together to achieve better moisture resistance and structural stability of the product.

[0025] In addition, the present application also provides a method for preparing the moisture-resistant positive electrode material, comprising the following steps: 1+a Ni x Co y Mn z M aO2 is mixed with a cobalt source, a lithium source, and an L-containing compound and then calcined. After the calcination, it is mixed with R, sintered, and cooled to obtain a moisture-resistant positive electrode material.

[0026] In one embodiment, the calcination is performed at a temperature of 350-850° C. at a heating rate of 1-5° C. / min for 2-10 hours.

[0027] In one embodiment, the sintering is performed at a temperature of 300-750° C. at a heating rate of 1-5° C. / min for 2-10 hours.

[0028] In one embodiment, after the calcination is completed, the mixture is naturally cooled to room temperature and then mixed with R and sintered.

[0029] The inventors have found that when the above-mentioned temperature rise program is selected for calcination and sintering during the preparation process, it can ensure that the obtained product has excellent moisture resistance and electrochemical properties; avoid insufficient reaction due to too low a sintering temperature and the influence of too high a sintering temperature on the product particle size, morphology, structure, etc., thereby reducing the electrochemical properties of the product.

[0030] In one embodiment, the lithium source is selected from at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxide, lithium oxalate, and lithium acetate.

[0031] In one embodiment, the lithium source is selected from lithium acetate and / or lithium hydroxide.

[0032] In one embodiment, the cobalt source is selected from at least one of cobalt-containing hydroxides, oxyhydroxides, carbonates, and acetates.

[0033] In one embodiment, the L-containing compound is selected from at least one of L-containing oxides, L-containing phosphates, L-containing acetates, and L-containing hydroxides.

[0034] In one embodiment, the L-containing compound is selected from at least one of TiO2, CeO2, SnO2, and Al2O3.

[0035] The inventors have found that when the lithium source, cobalt source and L-containing compound are the above substances, they can better react with other substances to form an inner coating layer of spinel structure, thereby providing surface Ni for moisture-resistant positive electrode materials. 3+ Low-fraction and low-oxygen-deficient inner shell.

[0036] In addition, the present application also provides the use of the moisture-resistant positive electrode material in a battery.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] The present application provides a moisture-resistant positive electrode material prepared by selecting chemical substances in appropriate proportions. Specifically, the core material is a doped Li-ion hexagonal layered structure.1+a Ni x Co y Mn z M a O2; the inner coating layer is a lithium-deficient Li with a spinel structure b CoL f O2; the outer coating layer is a nanocomposite oxide layer including R. Specifically, by selecting specific chemical substances and forming a specific layered structure, the present invention achieves excellent moisture resistance and structural stability, ensuring good electrochemical performance, thereby reducing the material's requirements for low-humidity environments and lowering the cost of battery cell manufacturing. Furthermore, the preparation method of the moisture-resistant positive electrode material provided by the present invention is simple and easy to implement, requires minimal equipment, has strong process controllability, is low-cost, and is amenable to practical industrial production. It can be widely applied in battery preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG1 is a scanning electron microscope image of the product prepared in Example 1 before storage;

[0040] FIG2 is a scanning electron microscope image of the product prepared in Example 1 after storage;

[0041] FIG3 is a scanning electron microscope image of a commercially available Ni90-NCM material before storage;

[0042] Figure 4 is a scanning electron microscope image of the commercially available Ni90-NCM material after storage. DETAILED DESCRIPTION

[0043] In order to better illustrate the purpose, technical solutions and advantages of this application, this application will be further described below in conjunction with specific embodiments.

[0044] Unless otherwise specified, the reagents, methods and equipment used in this application are conventional reagents, methods and equipment in the art.

[0045] Example 1

[0046] The present invention provides a moisture-resistant positive electrode material. The moisture-resistant positive electrode material is a core-shell structure, which includes a core material, an inner coating layer and an outer coating layer in sequence. The chemical formula of the core material is Li 1.1 Ni 0.98 Co 0.01 Mn 0.01 Zr 0.1 O2, the chemical formula of the inner coating layer is Li 1.3 CoAl 0.4 O2, the outer coating layer includes R, and the R is Al2O3;

[0047] The molar ratio of the inner coating layer to the core material is 0.038, and the molar ratio of Al2O3 in the outer coating layer to the core material is 0.02;

[0048] The preparation method of the moisture-resistant positive electrode material is as follows: 8 kg Li 1.1 Ni 0.98 Co 0.01 Mn 0.01 Zr 0.1 After O2 is mixed evenly with 247.18gCo(OH)2, 54.29gAl2O3, and 228.53gCH3COOLi at high speed, the temperature is increased to 850℃ at 1℃ / min, calcined for 2h, and then naturally cooled to room temperature. Subsequently, the intermediate product that has been calcined and naturally cooled to room temperature is mixed evenly with 163.31gAl2O3 at high speed, the temperature is increased to 350℃ at 1℃ / min, sintered for 8h, and then naturally cooled to room temperature; the moisture-resistant positive electrode material is obtained.

[0049] Example 2

[0050] The present invention provides a moisture-resistant positive electrode material. The moisture-resistant positive electrode material is a core-shell structure, which includes a core material, an inner coating layer and an outer coating layer in sequence. The chemical formula of the core material is Li 1.02 Ni 0.75 Co 0.05 Mn 0.2 Al 0.02 O2, the chemical formula of the inner coating layer is Li 0.7 CoTi 0.1 O2, the outer coating layer includes R, and the R is WO3;

[0051] The molar ratio of the inner coating layer to the core material is 0.01, and the molar ratio of WO3 in the outer coating layer to the core material is 0.01;

[0052] The preparation method of the moisture-resistant positive electrode material is as follows: 8 kg Li 1.02 Ni 0.75 Co 0.05 Mn 0.2 Al 0.02 After O2 was mixed evenly with 106.43gCo(CH3COO)2, 4.80gTiO2 and 15.37gLi2CO3 at high speed, the temperature was increased to 720℃ at 5℃ / min and calcined for 8h, and then naturally cooled to room temperature. Subsequently, the intermediate product that had been calcined and naturally cooled to room temperature was mixed evenly with 174.97gWO3 at high speed, the temperature was increased to 500℃ at 2℃ / min, sintered for 10h, and then naturally cooled to room temperature to obtain a moisture-resistant positive electrode material.

[0053] Example 3

[0054] The present invention provides a moisture-resistant positive electrode material. The moisture-resistant positive electrode material is a core-shell structure, which includes a core material, an inner coating layer and an outer coating layer in sequence. The chemical formula of the core material is Li 1.05 Ni 0.50 Co 0.20 Mn 0.30 (Y.Na) 0.05 O2, the chemical formula of the inner coating layer is Li 1.1 Co(Ce.Sn) 0.02 O2, the outer coating layer includes R, and the R is TiO2 and Nb2O3;

[0055] The molar ratio of the inner coating layer to the core material is 0.02, and the molar ratio of the sum of the moles of TiO2 and Nb2O3 in the outer coating layer to the core material is 0.005;

[0056] The preparation method of the moisture-resistant positive electrode material is as follows: 8 kg Li 1.06 Ni 0.50 Co 0.20 Mn 0.30 (Y.Na) 0.03 After O2 was mixed evenly with 146.61gCoOOH, 5.49gCeO2, 4.81gSnO2 and 73.56gLiOH.H2O at high speed, the temperature was raised to 350℃ at 2℃ / min and calcined for 10h, and then naturally cooled to room temperature. Subsequently, the intermediate product after calcination and natural cooling to room temperature was mixed evenly with 31.85gTiO2 and 105.97gNb2O5 at high speed, the temperature was raised to 750℃ at 1℃ / min and sintered for 2h, and then naturally cooled to room temperature to obtain a moisture-resistant positive electrode material.

[0057] Example 4

[0058] The present embodiment provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and the embodiment 1 is that the chemical formula of the core material is Li 1.1 Ni 0.98 Co 0.01 Mn 0.01 Si 0.1 O2.

[0059] Example 5

[0060] The present embodiment provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and the embodiment 1 is that the chemical formula of the inner coating layer is Li 1.3 CoB 0.4 O2.

[0061] Example 6

[0062] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and the embodiment 1 is that the outer coating layer includes R, and R is La2O3.

[0063] Example 7

[0064] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that during the preparation process, lithium carbonate is used instead of lithium oxalate in step (1).

[0065] Example 8

[0066] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that during the preparation process, aluminum hydroxide is used instead of aluminum oxide in step (1).

[0067] Example 9

[0068] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the molar ratio of Al2O3 in the outer coating layer to the core material is 0.015.

[0069] Example 10

[0070] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the molar ratio of Al2O3 in the outer coating layer to the core material is 0.003.

[0071] Example 11

[0072] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the molar ratio of the inner coating layer to the core material is 0.045.

[0073] Example 12

[0074] The embodiment of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the molar ratio of the inner coating layer to the core material is 0.01.

[0075] Comparative Example 1

[0076] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the outer coating layer includes R, and R is MgF2.

[0077] Comparative Example 2

[0078] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the chemical formula of the inner coating layer is Li 1.3 CoNa0.4 O2.

[0079] Comparative Example 3

[0080] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the chemical formula of the core material is Li 1.1 Ni 0.98 Co 0.01 Mn 0.01 Ba 0.1 O2.

[0081] Comparative Example 4

[0082] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the chemical formula of the inner coating layer is Li 1.6 CoAl 0.3 O2.

[0083] Comparative Example 5

[0084] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that the molar ratio of Al2O3 in the outer coating layer to the core material is 0.04.

[0085] Comparative Example 6

[0086] The comparative example of the present application provides a moisture-resistant positive electrode material, the only difference from Example 1 being that the molar ratio of the inner coating layer to the inner core is 0.05.

[0087] Comparative Example 7

[0088] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that during the preparation process, the temperature is raised to 850° C. at 8° C. / min and calcined for 2 hours, and then naturally cooled to room temperature.

[0089] Comparative Example 8

[0090] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that during the preparation process, the temperature is raised to 1000° C. at 1° C. / min and calcined for 2 hours, and then naturally cooled to room temperature.

[0091] Comparative Example 9

[0092] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that during the preparation process, the temperature is raised to 350° C. at 0.2° C. / min, sintered for 8 hours, and then naturally cooled to room temperature.

[0093] Comparative Example 10

[0094] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 1 is that during the preparation process, the temperature is raised to 200° C. at 1° C. / min, sintered for 8 hours, and then naturally cooled to room temperature.

[0095] Comparative Example 11

[0096] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 2 is that it does not include an outer coating layer. The specific preparation method is: 8 kg Li 1.02 Ni 0.75 Co 0.05 Mn 0.2 Al 0.02 After O2 was uniformly mixed with 106.43gCo(CH3COO)2, 4.80gTiO2 and 15.37g Li2CO3 at high speed, the temperature was raised to 720℃ at 5℃ / min and calcined for 8h, and then naturally cooled to room temperature to obtain a moisture-resistant positive electrode material.

[0097] Comparative Example 12

[0098] The comparative example of the present application provides a moisture-resistant positive electrode material. The only difference between the moisture-resistant positive electrode material and Example 2 is that it does not include an inner coating layer. The specific preparation method is: 8 kg Li 1.02 Ni 0.75 Co 0.05 Mn 0.2 Al 0.02 After O2 and 174.97g WO3 were mixed uniformly at high speed, the temperature was raised to 500°C at 2°C / min, sintered for 10 hours, and then naturally cooled to room temperature to obtain a moisture-resistant positive electrode material.

[0099] Effect Examples

[0100] This effect example verifies the moisture-resistant positive electrode materials prepared in Examples 1-12 and Comparative Examples 1-12 and the commercially available positive electrode material products Ni90-NCM (LiNi 0.9 Co 0.05 Mn 0.05 O2), 712NCM(LiNi 0.7 Co 0.1 Mn 0.2 O2), 523NCM(LiNi 0.5 Co 0.2 Mn 0.3 O2) performance; specifically, the above materials were placed in the same environment for 2 days and then tested, the humidity of the environment was 40%; the test items included the following aspects:

[0101] 1. Moisture: The test instrument is a coulometric moisture meter, and the test method is Karl Fischer coulometric titration;

[0102] 2. Residual lithium: The testing instrument is a potentiometric titrator, and the testing method is chemical reagent potentiometric titration;

[0103] 3. Soft pack performance evaluation: NCM and PVDF (polyvinylidene fluoride) are used as binders, activated carbon is used as a conductive agent, and the mass percentage of the three is 96:2:2. NMP (N-methylpyrrolidone) is used as a solvent. The mixture is stirred into a slurry, and the slurry is evenly coated on aluminum foil using a coating machine. After drying, it is made into a positive electrode sheet. The electrolyte is 1.02 mol / L lithium hexafluorophosphate, DMC (dimethyl carbonate) / EMC (ethyl methyl carbonate) / PC (polycarbonate) as the electrolyte solvent, and graphite is used as the negative electrode to make a soft pack battery. The above battery is formed into a lithium-ion battery. After aging, the battery's discharge capacity, cycle performance under different current conditions, and storage performance are tested. Specifically:

[0104] (1) Discharge capacity: First charge to 4.4 V at 0.33 C, constant voltage to 0.05 C, and discharge to 2.8 V at 1 C at 20 ° C, and record it as the initial discharge capacity in grams;

[0105] (2) Room temperature cycling performance: In the voltage range of 2.8-4.4V, in a 25°C constant temperature box, the battery is charged at 1C and discharged at 1C until its capacity retention rate reaches 80%;

[0106] (3) High temperature cycling performance: In the voltage range of 2.8-4.4V, in a 45°C constant temperature box, the battery is charged at 1C and discharged at 1C until its capacity retention rate reaches 80%;

[0107] (4) High-temperature storage performance: The battery cell was fully charged to 4.4V, and then placed in a 60°C oven for 30 days. The volume change of the battery cell before and after baking was recorded, and the volume change rate was recorded. Volume change rate = (volume of the battery cell after baking - volume of the battery cell before baking) / volume of the battery cell before baking × 100%; then the battery cell was discharged at 1C to 2.8V, and the discharge gram capacity was recorded. The ratio of the discharge gram capacity to the initial discharge gram capacity in (1) was recorded as the storage gram capacity retention rate. Storage gram capacity retention rate = (gram capacity after storage - initial gram capacity) / volume of the battery cell before baking × 100%;

[0108] The test results are shown in Table 1;

[0109] Table 1

[0110] As can be seen from Table 1, the product obtained by adopting the technical solution of the present application has excellent moisture resistance and electrochemical properties; specifically, after the product obtained by adopting the technical solution of the present application is placed in an environment with a humidity of 40% for 2 days, the moisture content is less than 0.0715%, the residual lithium is less than 0.2590%, the discharge capacity is above 184 mAh / g, the number of normal temperature cycles is more than 1050 cycles, the number of high temperature cycles is more than 600 cycles, the high temperature storage volume change rate is less than 40%, and the gram capacity retention rate is more than 70%. The products in Examples 1-3 are further specifically compared with commercially available products. Compared with Ni90-NCM, the product in Example 1 has obvious improvements in both moisture resistance and electrochemical performance. Specifically, compared with Ni90-NCM, the moisture content is reduced by 56.36%, the residual lithium is reduced by 71.84%, the discharge capacity is increased by 13.86%, the number of normal temperature cycles is increased by 136.36%, the number of high temperature cycles is increased by 166.67%, the volume change rate is reduced by 70.59%, and the gram capacity retention rate is increased by 37.93%; comparing the product in Example 2 with 712NCM and the product in Example 3 with 523NCM, it can be found that whether it is moisture resistance or electrochemical performance, the products in the embodiments of the present application have achieved significant results compared with commercial products close to Ni; further illustrating that the moisture-resistant positive electrode material provided by the present application effectively reduces the surface Ni through the three-layer structure 3+ ratio and oxygen deficiency and reduction of Li + Reacts with hydroxyl groups, making the material have good moisture resistance and electrochemical properties. Figures 1 and 2 are electron microscope images of Example 1 before and after storage, from which it can be seen that a small amount of residual lithium is generated on the surface of the Example 1 material after storage; Figures 3 and 4 are SEM images of commercially available Ni90-NCM materials before and after storage, from which it can be seen that a large amount of residual lithium is generated on the surface of the material after storage, which fully demonstrates that Example 1 has good moisture resistance and inhibits the Li + It undergoes an exchange reaction with water in the environment to generate residual lithium.

[0111] It can be seen from Example 1, Examples 4-6 and Comparative Examples 1-3 that the selection of M, L and R in the moisture-resistant positive electrode material will also affect the moisture resistance and electrochemical performance of the product.

[0112] It can be seen from Example 1 and Examples 7-8 that the lithium source and the form of the L-containing compound selected during the preparation process will also affect the performance of the product; when the lithium source is lithium carbonate or the N-containing compound is in the form of a N-containing oxide, the overall effect of the obtained product is more excellent.

[0113] It can be seen from Example 1, Examples 9-10 and Comparative Example 5 that when the molar ratio of R in the outer coating layer to the inner core layer is too large, the gram capacity of the obtained product is low, and the product impedance is too large, resulting in poor cycle performance; it can be seen from Example 1, Examples 11-12 and Comparative Example 6 that when the molar ratio of the inner coating layer to the inner core layer is too large, the cycle performance of the obtained product is poor compared with Example 1.

[0114] It can be seen from Example 1 and Comparative Examples 7-10 that the parameters in the preparation process will also affect the overall performance of the product.

[0115] It can be seen from Example 2 and Comparative Examples 11-12 that regardless of the lack of an inner coating layer or an outer coating layer, the moisture resistance of the obtained product is significantly reduced, and the electrochemical performance also shows a downward trend; compared with Example 2, the moisture content of Comparative Examples 11-12 increased by 26.42-68.11%, the residual lithium increased by 277.18-396.91%, the discharge capacity decreased by 8.42%, the number of normal temperature cycles decreased by 30-37%, the number of high temperature cycles decreased by 29.17-33.33%, the high temperature storage volume change rate increased by 50-60%, and the high temperature storage gram capacity retention rate decreased by 7.61-13.04%; this shows that the inner coating layer and the outer coating layer in the present application can work synergistically, so that the product as a whole achieves better moisture resistance and electrochemical performance.

Claims

1. A moisture-resistant positive electrode material, characterized in that: The moisture-resistant positive electrode material is a core-shell structure, which includes a core material, an inner coating layer and an outer coating layer in sequence; the chemical formula of the core material is Li 1+a Ni x Co y Mn z M a O2, the chemical formula of the inner coating layer is Li b CoL f O2, the outer coating layer includes R; Among them, 0.50≤x≤0.98, 0.01≤y≤0.2, 0.01≤z≤0.49, 0 <a≤0.1,x+y+z=1; 0 <b≤1.3,0<f≤0.4,0.5<b / (1+f)<0.99; M is selected from at least one of Na, K, Mg, Al, Ti, Zr, Sr, Y, Ce, W, La, Sn, Mo, Fe, B, and Si; L is at least one selected from Al, Ti, W, B, Nb, Sb, F, Sn, Ce, and Mg; R is selected from at least one of La2O3, MoO3, WO3, TiO2, Nb2O5, B2O3, and Al2O3.

2. The moisture-resistant positive electrode material according to claim 1, characterized in that: The moisture-resistant positive electrode material at least meets the following conditions: (a) the inner core has a hexagonal layered structure and a space group of (R-3m); (b) the inner coating layer has a spinel structure; (c) The outer coating layer is a nanocomposite oxide layer.

3. The moisture-resistant positive electrode material according to claim 1, characterized in that: The molar ratio of the inner coating layer to the inner core is ≤0.

045.

4. The moisture-resistant positive electrode material according to claim 1, characterized in that: The molar ratio of the inner coating layer to the inner core is 0.01-0.

038.

5. The moisture-resistant positive electrode material according to claim 1, characterized in that: The molar ratio of R in the outer coating layer to the inner core is ≤0.

02.

6. The moisture-resistant positive electrode material according to claim 1, characterized in that: The molar ratio of R in the outer coating layer to the inner core is 0.005-0.

02.

7. The method for preparing a moisture-resistant positive electrode material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Li 1+a Ni x Co y Mn z M a O2 is mixed with a cobalt source, a lithium source, and a compound containing L, and then calcined. After the calcination, it is mixed with R, sintered, and cooled to obtain a moisture-resistant positive electrode material.

8. The preparation method according to claim 7, characterized in that: The calcination is carried out at a temperature of 350-850° C. at a heating rate of 1-5° C. / min for 2-10 hours.

9. The preparation method according to claim 7, characterized in that: The sintering is performed at a temperature of 300-750° C. for 2-10 hours at a heating rate of 1-5° C. / min.

10. The preparation method according to claim 7, characterized in that: After the calcination is completed, the mixture is naturally cooled to room temperature and then mixed with R and sintered.

11. The preparation method according to claim 7, characterized in that: The lithium source is selected from at least one of lithium carbonate, lithium nitrate, lithium hydroxide, lithium oxide, lithium oxalate and lithium acetate.

12. The preparation method according to claim 7, characterized in that: The cobalt source is selected from at least one of cobalt-containing hydroxides, oxyhydroxides, carbonates and acetates.

13. The preparation method according to claim 7, characterized in that: The L-containing compound is selected from at least one of L oxides, L-containing phosphates, L-containing acetates, and L-containing hydroxides.

14. The preparation method according to claim 7, characterized in that: The L-containing compound is selected from at least one of TiO2, CeO2, SnO2, and Al2O3.

15. Use of the moisture-resistant positive electrode material according to any one of claims 1 to 6 in a battery.

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