Positive active material coated with a composite organic layer and preparation and use thereof

Abstract

The present invention belongs to the field of battery electrode materials and specifically relates to a method for preparing a positive electrode active material coated with a composite organic layer. The method comprises partially neutralizing a chelated organic acid with an alkaline substance containing a metal M, and exchanging the acidic hydrogen ions in the chelated organic acid with the M ions to obtain a modified chelated organic acid. The pH at the end point of the neutralization reaction is 4 to 7, and the M is Li or Na. The modified chelated organic acid is mixed with a positive electrode active material containing the M element and subjected to a first-stage coating modification to obtain a first-stage coated modified material. The first-stage coated modified material is then placed in an atmosphere containing a titanate coupling agent for a second-stage vapor-phase coating modification to obtain the composite organic layer-coated positive electrode active material. The present invention also includes materials produced by the preparation method and their applications. The method can effectively improve the rate capability and stability of the prepared material under high current conditions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of battery electrode materials, and particularly relates to the technical field of positive electrode active materials. BACKGROUND

[0002] From the perspective of resource guarantee, cost and energy density, in the battery system meeting >350Wh / kg, high-capacity lithium-rich manganese-based oxide positive electrode material xLi2MnO3·(1-x)LiTMO2(TM=Ni, Co, Mn) (0 2- ) is the most promising candidate for future application. For lithium-rich manganese-based positive electrode material, its high capacity is derived from the participation of transition metal cations and oxygen anions (O

[0003] Surface coating technology is an effective means to improve the performance of battery materials. It mainly has the following effects: (1) when the charge cutoff potential is high, it can improve the cycle stability of the material; (2) improve the thermal stability and charge-discharge performance of the material under large current; (3) effectively improve the interface effect of the material, thereby reducing the internal resistance of the battery. Surface coating can prevent direct contact between the positive electrode material and the electrolyte, thereby avoiding capacity decay caused by side reactions between the positive electrode material and the electrolyte, and improving the safety of the battery at high temperature. Surface coating helps to stabilize the positive electrode / electrolyte interface, but the interface ion transport and interface compatibility in long cycle become a challenge.

[0004] Generally, surface coating by oxides, fluorides or phosphates can reduce oxygen evolution and avoid direct contact of the surface with acidic substances in the electrolyte. Commonly used inorganic substances are generally electrochemically inert, which is not conducive to the diffusion of lithium ions at the interface, resulting in a decrease in the active sites of the material. Most of the current surface coating methods present inert particle point decoration coating, and it is difficult to achieve continuous and uniform distribution of the surface coating and construction of the functional coating layer, and it is difficult to ensure the stability of the coating thickness and the interface structure. Generally, the poor conductivity and electrochemical inertness of the coating layer inevitably affect the rate performance and reversible capacity of the positive electrode material, and have a weak inhibitory effect on the strain deformation of the active material. With the long-term electrochemical cycling, the surface hetero-layer is difficult to maintain conformality, and cannot effectively overcome the damage of volume change to the positive electrode material, resulting in the failure of the surface modification. SUMMARY

[0005] In view of the problems of unsatisfactory coating effect and electrochemical performance of the existing organic material coated positive electrode active material, the first object of the present application is to provide a preparation method of a composite organic layer coated positive electrode active material, aiming to improve the ionic conductivity and hydrophobicity of the coated material, and further improve its electrochemical performance, especially the cycle stability.

[0006] The second object of the present application is to provide a composite organic layer coated positive electrode active material prepared by the preparation method and its application in alkali metal batteries.

[0007] The third object of the present application is to provide an alkali metal secondary battery comprising the composite organic layer coated positive electrode active material.

[0008] The preparation method of the composite organic layer coated positive electrode active material comprises the following steps:

[0009] Step (1):

[0010] The chelating organic acid is subjected to neutralization reaction with an alkaline substance containing metal M, and the pH at the end of the neutralization reaction is controlled to be 4-7, so that part of the hydrogen ions in the chelating organic acid are replaced by metal M, to obtain modified chelating organic acid; the M is Li or Na;

[0011] Step (2):

[0012] The modified chelating organic acid and the positive electrode active material containing M element are mixed to perform first-stage coating modification, to obtain first-stage coating modified material;

[0013] Step (3):

[0014] The first-stage coating modified material is placed in an atmosphere containing titanate coupling agent to perform gas-phase second-stage coating modification, to obtain the composite organic layer coated positive electrode active material.

[0015] In the application, the hydrogen ions in the chelating organic acid are ion exchanged into M ions by modification, and then the positive active material is coated and modified in the first stage, and then coated and modified in the second stage by using a titanium ester coupling agent atmosphere, so that the stability and uniformity of the organic coating can be unexpectedly improved, and the cycle stability of the modified positive active material can be improved.

[0016] In the application, the modification of the chelating organic acid and the first stage modification and the second stage gas phase coating modification by the titanium ester coupling agent are combined to improve the electrochemical performance of the coated and modified positive active material.

[0017] In the application, the hydrogen ions in the chelating organic acid are at least one of carboxylate hydrogen ions and phosphate hydrogen ions.

[0018] Preferably, the chelating organic acid is at least one of phytic acid and EDTA.

[0019] In the application, the basic substance containing metal M is at least one of hydroxides and carbonates of M. For example, it can be sodium hydroxide, lithium hydroxide, lithium carbonate or sodium carbonate.

[0020] In the application, the pH at the end point of the neutralization reaction system can be further controlled to be 4-6, and can be further controlled to be 4.5-5.

[0021] In the application, the type of the positive active material is an oxide positive material. For example, the chemical expression of the positive active material is at least one of MXO2 and MY2O4.

[0022] The M is Li or Na.

[0023] The X and Y are at least one of Ni, Co and Mn.

[0024] Preferably, the positive active material is xLiXO2·(1-x)Li2XO3, wherein X is at least one of Ni, Co and Mn metal elements, and 0

[0025] In the application, the first stage coating modification method can be liquid phase coating, and the solvent is, for example, water or a mixed solvent of water and an organic solvent.

[0026] In the application, an example of the liquid phase coating step is that the positive active material containing M elements is placed in the neutralization reaction system for the first stage coating, and then solid-liquid separation is performed to obtain a first stage coating modified material.

[0027] Preferably, the weight ratio of the modified chelating organic acid and the positive electrode active material containing M element is 0.3% to 1.5%, and further can be 0.5 to 1%.

[0028] In the present application, the temperature of the first-stage coating modification process is not particularly required, for example, can be 10 to 70℃, and considering the simplicity of the technical solution, can be further room temperature.

[0029] In the present application, the time of the first-stage coating modification is not particularly required, for example, can be more than 1h, and further can be 2 to 5h.

[0030] In the present application, after the completion of the first-stage coating modification, solid-liquid separation is carried out, and then drying treatment is carried out to obtain a first-stage coating material. The temperature of the drying treatment can be, for example, more than 50℃, and further can be 60 to 90℃. The time of the drying is not particularly required, for example, can be more than 6h, and further can be 12 to 24h.

[0031] In the present application, the first-stage coating is carried out by using the modified chelating organic acid in advance, which can uniformly and closely coat the chelating organic acid on the surface of the positive electrode active material based on chemical and physical actions such as hydrogen bond, and further cooperates with the gas-phase coating idea under the participation of the titanate coupling agent, so as to unexpectedly realize the synergy, improve the uniformity and tightness of the coating structure, and further improve the stability of the modified positive electrode active material.

[0032] In the present application, the titanate coupling agent can be at least one of the titanate coupling agents known in the industry, for example, can include mono-oxygen alkyl phosphate titanate coupling agent, mono-oxygen alkyl pyrophosphate titanate coupling agent, and pyrophosphoric acid acyloxy titanate coupling agent.

[0033] Further, the titanate coupling agent includes at least one of isopropyl tri(dioctyl pyrophosphoric acid acyloxy) titanate coupling agent (201), isopropyl tri(dioctyl phosphoric acid acyloxy) titanate coupling agent (102), and isopropoxy tri(dioctyl pyrophosphoric acid acyloxy) ethylene titanate coupling agent (311).

[0034] In the present application, the titanate coupling agent and the first-stage coating modification material are arranged in the same or different regions of the same closed container, the closed container is heated, the titanate coupling agent is volatilized, and the first-stage coating modification material is subjected to second-stage coating modification in the atmosphere of the titanate coupling agent.

[0035] Preferably, the weight percentage of the titanate coupling agent and the positive electrode active material containing M element is 5% to 50%, further is 15 to 35%, and further can be 19 to 22%;

[0036] Preferably, the temperature of the second-stage coating modification stage is greater than or equal to the volatilization temperature T of the titanate coupling agent and less than or equal to 1.2T; in the present application, the temperature of the second-stage coating modification stage can be specifically 210-250°C.

[0037] Preferably, the time of the second-stage coating modification is 0.5-3h, and can further be 1-2h.

[0038] The present application also provides the composite organic layer-coated positive electrode active material prepared by the preparation method.

[0039] In the present application, the preparation method can impart special interface characteristics to the material, and the material with the characteristics prepared by the preparation method can unexpectedly exhibit better cycle stability.

[0040] In the present application, the positive electrode active material core, the chelating organic acid layer modified on the core by a chemical method, and the titanate coupling agent layer modified on the chelating organic acid layer by hydrogen bonding;

[0041] In the composite organic layer-coated positive electrode active material, the content of the positive electrode active material is 98-99.5wt.%, and can further be 98.5-99.5%. In the present application, good coating stability and uniformity can be obtained at a low content of coated organic components, and excellent electrochemical performance can be exhibited.

[0042] The present application also provides the application of the composite organic layer-coated positive electrode active material prepared by the preparation method, which is used as a positive electrode active material to prepare an alkali metal M secondary battery.

[0043] In the present application, the modified positive electrode active material can be used to prepare a desired alkali metal M secondary battery by conventional means. For example, the modified positive electrode active material is compounded with a conductive agent and a binder to form a positive electrode, and then the battery is assembled with a separator and a negative electrode.

[0044] In the present application, the metal M secondary battery is, for example, an ion battery of metal M.

[0045] The present application also provides an alkali metal M secondary battery comprising the composite organic layer-coated positive electrode active material prepared by the preparation method.

[0046] Preferably, the positive electrode comprises the composite organic layer-coated positive electrode active material.

[0047] In the present application, the hydrogen in the modified chelating organic acid can exchange with lithium ions on the surface of the positive active material to form lithium defects, and form a coating layer of M salt of the complex organic acid on the surface of the positive active material, and then perform a second-stage gas-phase coating treatment, so that the titanium ester coupling agent in the gas phase forms a hydrogen bond with the acid radical group in the M salt of the complex organic acid through its hydroxyl group, making the compounding more uniform, the structure more stable, and the corrosion resistance in high voltage and electrolyte stronger.

[0048] Advantages

[0049] The present application modifies the chelating organic acid in advance, partially ion-exchanges the hydrogen ions into M ions, then performs a first-stage coating modification on the positive active material, and then performs a second-stage coating modification in a titanium ester coupling agent atmosphere, so that the stability and uniformity of the organic coating are unexpectedly improved, and the cycle stability of the modified positive active material is improved. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 SEM image of the lithium-rich manganese-based positive active material before coating of Example 1 (also referred to as Comparative Example 1);

[0051] Figure 2 SEM image of the co-coated lithium-rich manganese-based positive active material prepared in Example 1.

[0052] Figure 3 Capacity cycle comparison chart of the battery assembled before and after coating of Example 1 at 1C rate.

[0053] Figure 4 Capacity cycle comparison chart of the battery assembled from the positive active materials of Example 1 and Comparative Example 2 at 1C rate.

[0054] Figure 5 Capacity comparison chart of the battery assembled from the positive active materials of Example 1 and Comparative Example 1 at different rates of 0.1-5C.

[0055] Figure 6 SEM image of the co-coated lithium-rich manganese-based positive active material prepared in Example 2. DETAILED DESCRIPTION

[0056] The test method of the electrochemical performance of the present application is, for example:

[0057] In the present application, the temperature of the first-stage modification process can be room temperature, for example, 20-40℃.

[0058] In the present application, in the first modification process, the titanate and the first coating material can be heated together in the form of a mixture for gas phase coating (first coating idea), or the first coating material and the titanate can be placed in different areas of the same reaction vessel and then heated together for volatilization coating (second coating idea). In the following cases, the first coating idea is used unless otherwise stated.

[0059] In the present application, the type of active material to be coated and modified is not particularly limited, for example, it can be any known active material. In the following cases, lithium-rich manganese-based material is used as a typical embodiment.

[0060] The coated and modified positive electrode active material, conductive carbon black and PVDF were mixed and ground in a marquis mortar by hand for 20 min at a weight ratio of active ingredient: conductive agent: binder = 8:1:1, NMP was added, and a positive electrode slurry was prepared. The prepared slurry was coated on an 18 μm thick aluminum foil, dried at 120°C under vacuum, and then punched into an electrode sheet with a diameter of 14 mm. A 2025 button cell was assembled using Cellgard 2400 as the separator (diameter 19 mm) and LiPF6 (solvent EC / DMC / EMC, volume ratio 1:1:1) as the electrolyte. The charge and discharge voltage range was 2.0-4.8 V, and the capacity retention rate after 100 cycles at room temperature, and the specific capacity at different rates from 0.1C to 5C at room temperature were measured at 1C (1C = 250 mAh g -1 ).

[0061] Example 1

[0062] Step (1):

[0063] Accurately weigh 0.05 g of phytic acid solution, an appropriate amount of lithium hydroxide and an appropriate amount of deionized water, and stir until uniform to obtain a mixed solution A (pH 5);

[0064] Step (2): First modification

[0065] 10 g of lithium-rich manganese-based lithium acid (Li 1.2 Ni 0.2 Mn 0.6 O2) was dispersed in 10 mL of isopropanol and stirred for 20 min to obtain a suspension B. The A solution was added to the B suspension and stirred for 3 hours. The obtained solid-liquid mixture was filtered, the filter cake was placed in a 70°C oven for 12 hours, and the solvent was evaporated to obtain material C;

[0066] Step (3): Second modification

[0067] Accurately weigh 2 g of isopropyl tri(dioctyl pyrophosphato) titanate 201, place it in an alumina crucible, and put it into a tube furnace together with material C, vacuumize, heat at a rate of 3°C / min to 220°C and keep for 1 h to obtain co-coated sample 1. The coating amount of organic components is 1%. The SEM image is shown in Figure 2 .

[0068] Determine its charge-discharge cycle at 1C (1C = 250 mAh g -1 ) for 100 times, and the capacity retention rate is 96%; the capacity at 5C can reach 120 mAh g -1 .

[0069] Comparative Example 1

[0070] Compared with Example 1, the only difference is that the lithium-rich manganese-based lithium acid in it is not coated.

[0071] Determine its charge-discharge cycle at 1C for 100 times, and the capacity retention rate is 88%;

[0072] Comparative Example 2

[0073] Compared with Example 1, the only difference is that step (3) is not performed, and the ratio of step 2 positive electrode material and phytic acid is adjusted so that the organic coating amount of the coated material is the same as the total organic coating amount of sample 1 of Example 1. Determine its charge-discharge cycle at 1C for 100 times, and the capacity retention rate is 91%;

[0074] Comparative Example 3

[0075] Compared with Example 1, the only difference is that steps (1) and (2) are not performed, but the lithium-rich manganese-based lithium acid is directly subjected to step (3) treatment, and the organic coating amount of the coated material is controlled to be the same as the total organic coating amount of sample 1 of Example 1. Determine its charge-discharge cycle at 1C for 100 times, and the capacity retention rate is 85%.

[0076] Comparative Example 4

[0077] Compared with Example 1, the only difference is that the modification treatment of step (1) is not performed, that is, in step (1), the lithium hydroxide is not added, and the other operations and parameters are the same as Example 1. Determine its charge-discharge cycle at 1C for 100 times, and the capacity retention rate is 76%.

[0078] Comparative Example 5

[0079] Compared with Example 1, the only difference is that step (3) uses liquid coating method, and the steps are as follows: 0.1 g of isopropyl tris (dioctyl pyrophosphoryloxy) titanate 201, 10 g of lithium-rich manganese-based lithium acid are accurately weighed, isopropyl tris (dioctyl pyrophosphoryloxy) titanate 201 is dissolved in an appropriate amount of isopropyl alcohol, lithium-rich manganese-based lithium acid is added, and stirring and drying are carried out at 70°C to obtain a sample with the same amount of organic coating as Example 1. The capacity retention rate is 75% after 100 times of charge-discharge cycles at 1C.

[0080] Comparative Example 6

[0081] Compared with Example 1, the only difference is that the processing order is changed, that is, the lithium-rich manganese-based lithium acid is first coated with titanate by step (3), and then steps (1) and (2) are sequentially performed. The proportions of the components and the conditions are the same as in Example 1. The capacity retention rate is 82% after 100 times of charge-discharge cycles at 1C.

[0082] Example 2

[0083] 0.05 g of ethylenediaminetetraacetic acid, an appropriate amount of lithium hydroxide and an appropriate amount of deionized water are accurately weighed and stirred uniformly to obtain a mixed solution A (pH is 4.5); 10 g of lithium-rich manganese-based lithium acid (same as in Example 1) is dispersed in 10 mL of isopropyl alcohol and stirred for 20 min to obtain a suspension B. The A solution is added to the B suspension and stirred for 3 hours, and the obtained solid-liquid mixture is suction filtered, the filter cake is placed in a 70°C oven, and the solvent is evaporated for 12 hours to obtain material C; 2 g of isopropyl tris (dioctyl phosphoric acid acyloxy) titanate 102 is accurately weighed and placed in an alumina crucible, and then placed in a tube furnace together with material C, vacuumized, heated at a rate of 3°C / min to 240°C and kept for 1 h to obtain a co-coating treatment sample 2. The SEM is shown in Figure 6 . And Figure 1 It can be seen that there is a composite coating layer on the surface.

[0084] The capacity retention rate is 95% after 100 times of charge-discharge cycles at 1C (1C = 250 mAh g -1 ).

[0085] Example 3

[0086] Accurately weigh 0.05 g of ethylenediamine tetraacetic acid, an appropriate amount of lithium hydroxide and an appropriate amount of deionized water, stir uniformly to obtain a mixed solution A (pH is 4.5); 10 g of lithium-rich manganese-based lithium acid (same as example 1) is dispersed in 10 mL of isopropyl alcohol, stirred and dispersed for 20 min to obtain a suspension B. The A solution is added to the B suspension under continuous stirring for 3 hours, and the obtained solid-liquid mixture is suction filtered. The filter cake is placed in a 70°C oven for 12 hours, and the solvent is evaporated to obtain material C; accurately weigh 2 g of isopropyl tris (dioctyl pyrophosphoric acyloxy) titanate 201, place it in an alumina crucible, and put it into a tube furnace together with material C. Vacuumize, heat at a rate of 3°C / min to 210°C and keep for 1 h to obtain a co-coated sample 3.

[0087] Determine the charge-discharge cycle at 1C (1C = 250 mA / g -1 ) for 100 times, and the capacity retention rate is 96%;

[0088] Example 4

[0089] Accurately weigh 0.05 g of phytic acid solution, an appropriate amount of lithium hydroxide and an appropriate amount of deionized water, stir uniformly to obtain a mixed solution A (pH is 5); 10 g of lithium-rich manganese-based lithium acid (same as example 1) is dispersed in 10 mL of isopropyl alcohol, stirred and dispersed for 20 min to obtain a suspension B. The A solution is added to the B suspension under continuous stirring for 3 hours, and the obtained solid-liquid mixture is suction filtered. The filter cake is placed in a 70°C oven for 12 hours, and the solvent is evaporated to obtain material C; accurately weigh 2 g of isopropyl tris (dioctyl pyrophosphoric acyloxy) ethylene titanate 311, place it in an alumina crucible, and put it into a tube furnace together with material C. Vacuumize, heat at a rate of 3°C / min to 250°C and keep for 1.5 h to obtain a co-coated sample 4.

[0090] Determine the charge-discharge cycle at 1C (1C = 250 mA / g -1 ) for 100 times, and the capacity retention rate is 95%.

[0091] Example 5

[0092] Compared with example 1, the only difference is that in step (1), sodium hydroxide is used instead of lithium hydroxide, and the pH is controlled at 4.5; in step 2, the weight ratio of sodium ion manganese-based oxide positive material (Na 0.6 [Li 0.2 Mn 0.8 ]O2) and phytic acid is 1:0.1; in step 3, the weight ratio of 201 and sodium ion manganese-based oxide positive material is 0.15:1, and other operations and parameters are the same as example 1.

[0093] Determine the charge-discharge cycle at 100 mA / g for 100 times, and the capacity retention rate is 94.5%.

Claims

1. A method for preparing a positive electrode active material coated with a composite organic layer, characterized in that the steps include: Step (1): A chelated organic acid is partially neutralized with an alkaline substance containing a metal M, and the acidic hydrogen ions in the chelated organic acid are ion-exchanged with the M ions to obtain a modified chelated organic acid; wherein the pH at the end point of the neutralization reaction is 4 to 7, the M is Li or Na, and the acidic hydrogen ions in the chelated organic acid are at least one of carboxylate hydrogen ions and phosphate hydrogen ions; Step (2): The modified chelated organic acid and the positive electrode active material containing the M element are mixed to perform a first-stage coating modification to obtain a first-stage coating modified material; Step (3): The first stage coating modified material is placed in an atmosphere containing a titanate coupling agent to carry out a second stage gas phase coating modification to obtain the composite organic layer coated positive electrode active material.

2. The method for preparing a positive electrode active material coated with a composite organic layer according to claim 1, wherein: The chelated organic acid is at least one of phytic acid and EDTA.

3. The method for preparing a positive electrode active material coated with a composite organic layer according to claim 1 or 2, characterized in that: The alkaline substance containing metal M is at least one of a hydroxide and a carbonate of M.

4. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The chemical expression of the positive electrode active material is at least one of MXO2 and MY2O4; The M is Li or Na; The X and Y are at least one of Ni, Co and Mn.

5. The method for preparing a positive electrode active material coated with a composite organic layer according to claim 1, wherein: The positive electrode active material is xLiXO2·(1-x)Li2XO3, wherein X is at least any one of Ni, Co, and Mn metal elements, and 0<x<1.

6. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The first stage of coating modification is liquid phase coating; The liquid phase coating step is: placing the positive electrode active material containing the M element in the neutralization reaction system for the first stage of coating, followed by solid-liquid separation to obtain a first stage of coated modified material.

7. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The weight ratio of the modified chelated organic acid to the positive electrode active material containing the M element is 0.3% to 1.5%.

8. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The titanate coupling agent includes at least one of a monooxyalkyl phosphate titanate coupling agent, a monooxyalkyl pyrophosphate titanate coupling agent, and a pyrophosphate acyloxy titanate coupling agent.

9. The method for preparing a composite organic layer-coated positive electrode active material according to claim 8, wherein: The titanate coupling agent includes at least one of isopropyl tris (dioctyl pyrophosphate acyloxy) titanate coupling agent, isopropyl tris (dioctyl pyrophosphate acyloxy) titanate coupling agent and isopropoxy tris (dioctyl pyrophosphate acyloxy) ethylene titanate coupling agent.

10. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The titanate coupling agent and the first stage coating modified material are placed in the same or different areas of the same sealed container, the sealed container is heated to volatilize the titanate coupling agent, and the first stage coating modified material is subjected to the second stage coating modification in the atmosphere of the titanate coupling agent.

11. The method for preparing a positive electrode active material coated with a composite organic layer according to claim 1, wherein: The weight percentage of the titanate coupling agent and the positive electrode active material containing the M element is 5% to 50%.

12. The method for preparing a composite organic layer-coated positive electrode active material according to claim 11, wherein: The weight percentage of the titanate coupling agent and the positive electrode active material containing the M element is 15-35%.

13. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The temperature of the second coating modification stage is greater than or equal to the volatilization temperature T of the titanate coupling agent, and less than or equal to 1.2T.

14. The method for preparing a composite organic layer-coated positive electrode active material according to claim 1, wherein: The time for the second coating modification is 0.5~3h.

15. A positive electrode active material coated with a composite organic layer obtained by the preparation method according to any one of claims 1 to 14; The positive electrode active material includes a core, a chelated organic acid layer chemically modified on the core, and a titanate coupling agent layer modified on the chelated organic acid layer based on hydrogen bonding; In the positive electrode active material coated by the composite organic layer, the content of the positive electrode active material is 98-99.5 wt.%.

16. An application of the composite organic layer-coated positive electrode active material obtained by the preparation method according to any one of claims 1 to 14, characterized in that: It is used as a positive electrode active material to prepare a secondary battery of alkali metal M.

17. A secondary battery of an alkali metal M, characterized in that: The positive electrode active material coated with the composite organic layer is prepared by the preparation method according to any one of claims 1 to 14.

18. The secondary battery of alkali metal M according to claim 17, characterized in that The positive electrode contains the positive electrode active material coated with the composite organic layer.

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