Ternary composite positive electrode material, preparation method, pole piece and battery

Abstract

The invention relates to a ternary composite positive electrode material which is characterized in that the ternary composite positive electrode material is of a core-shell structure, the core is a ternary material, the surface of the ternary material is porous, additives are arranged in pores and comprise molybdenum trioxide and polyaniline, the shell is nitrogen-doped porous carbon and tetrachloro-p-benzoquinone, the pores of the ternary material are R1, R2, R3, R4, R5, R6, R7, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8, R8 and R8, and the pore of the nitrogen-doped porous carbon is R2, the particle size of the molybdenum trioxide is D1, the particle size of the polyaniline is D2, and R1 > = D1 > = D2 > = R2. Through structural design and material optimization, the comprehensive performance of the lithium ion battery positive electrode material is remarkably improved, multiple defects in the prior art are overcome, and the lithium ion battery positive electrode material has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a ternary composite cathode material, a preparation method, an electrode sheet and a battery. Background Art

[0002] Lithium-ion batteries have been widely used in fields such as portable electronic devices, electric vehicles, and grid energy storage systems due to their high energy density, high working voltage, and long cycle life. However, existing lithium-ion battery cathode materials have problems such as limited capacity and low cycle life, making it difficult to meet the rapidly developing demands. In particular, the performance and stability of lithium-ion battery cathode materials are insufficient, severely restricting their further improvement in terms of high energy density and long cycle life.

[0003] High-nickel ternary materials have a high nickel content and high energy density of the battery. With the increasing requirements for energy density in the electric vehicle industry, the nickel content in the cathode material has gradually increased. However, with the increase in nickel content, the surface of high-nickel materials becomes more and more sensitive, easily absorbing moisture and carbon dioxide in the air and existing on the surface of the material in the form of residual alkalis such as lithium carbonate and lithium hydroxide. Higher residual alkalis will reduce the processing performance of the electrode sheet, and the gas generation behavior during the cycling process also increases. Along with long-term cycling, the surface stability further deteriorates. Summary of the Invention

[0004] For this reason, the present invention provides a ternary composite cathode material. Through the design of a core-shell structure, a porous active material is used as the core, and conductive molybdenum trioxide and polyaniline are added to improve conductivity and stability, and nitrogen-doped porous carbon and p-chloranil are coated on the outer layer. Such a structural design not only improves the specific capacity and cycle life of the material, but also effectively solves problems such as poor conductivity and insufficient rate performance in the prior art. By optimizing the pore size of the active material and the size of the nitrogen-doped porous carbon, the performance and stability of the lithium-ion battery are further improved, meeting the requirements of high energy density and long cycle life.

[0005] The present invention proposes a ternary composite cathode material, which is characterized in that it has a core-shell structure. The core is a ternary material, the surface of the ternary material is porous, additives are provided in the pores, the additives are molybdenum trioxide and polyaniline, the shell is nitrogen-doped porous carbon and p-chloranil. Among them, the pore of the ternary material is R1, the pore of the nitrogen-doped porous carbon is R2, the particle size of the molybdenum trioxide is D1, the particle size of the polyaniline is D2, and R1≥D1≥D2≥R2.

[0006] The weight ratio of the molybdenum trioxide particles to the polyaniline particles is (30-40) to (60-70).

[0007] The weight ratio of the nitrogen-doped porous carbon to the tetrachlorobenzoquinone is (60 to 70) to (30 to 40).

[0008] The particle size D1 of the molybdenum trioxide is 0.2 - 0.8 μm, and the particle size D2 of the polyaniline is 0.01 - 0.1 μm.

[0009] The thickness of the shell is 1 - 10 nm, and the additive accounts for 1 - 10 wt% of the total mass of the ternary composite cathode material.

[0010] R1 is 0.5 - 1 μm and R2 is 5 - 20 nm.

[0011] The preparation method of the ternary composite cathode material according to any one of the above includes: high-speed mechanical fusion of the ternary material, molybdenum trioxide, and polyaniline, so that the additive enters the pores to obtain the core of the ternary composite material; depositing nitrogen-doped polymerized porous carbon and tetrachlorobenzoquinone on the core of the ternary composite material, and then performing low-temperature calcination to obtain the ternary composite cathode material.

[0012] The process of depositing nitrogen-doped porous carbon and tetrachlorobenzoquinone includes: placing the core of the ternary composite material in a reactor, purging with a protective gas and a reducing gas, loading the powdered nitrogen-doped porous carbon and tetrachlorobenzoquinone through a carrier gas, and reacting at 100°C to 200°C for 40 min to 60 min.

[0013] The preparation process of the nitrogen-doped porous carbon includes: carbonizing the nitrogen-containing polymer organic matter in an inert atmosphere; the carbonization temperature is 600°C - 1000°C, the heating rate is 0.5°C / min - 5°C / min, and the carbonization time is 1 h - 48 h.

[0014] The present invention also provides a pole piece, which includes the ternary cathode material according to any one of the above or the ternary cathode material obtained by the preparation method of the ternary cathode material according to any one of the above.

[0015] The present invention also provides a battery, which includes the above pole piece.

[0016] To solve the above technical problems,

[0017] The above technical solutions of the present invention have the following advantages compared with the prior art:

[0018] 1. Improve electrical conductivity and ionic conductivity: In the present invention, molybdenum trioxide and polyaniline are added into the pores of the porous active material. As a conductive polymer, polyaniline has good electrical conductivity, chemical stability and mechanical properties. Molybdenum trioxide is an inorganic compound with high mechanical strength and positive temperature coefficient effect. By adding molybdenum trioxide into the pores of the active material, the anti-puncture safety performance of the battery can be improved. Moreover, when polyaniline accumulates around molybdenum trioxide, a continuous conductive network will be formed, improving the electrical conductivity of the battery. Since the resistance of the positive temperature coefficient material is small, at low or normal temperatures, it does not affect the overall impedance of the battery. If an internal short circuit occurs in the battery, a large amount of Joule heat is generated, causing the temperature inside the battery cell to rise. After the temperature exceeds the Curie point of molybdenum trioxide, the resistance of molybdenum trioxide increases, rapidly reducing the heat generation power of the internal short circuit, enabling the electrical energy of the battery to be released and reducing the risk of thermal runaway after the internal short circuit of the battery cell. Thus, the safety of the battery cell is improved.

[0019] 2. Nitrogen-doped porous carbon as a coating layer forms a multi-layer dense film on the surface of the ternary material. On the one hand, the nitrogen-doped porous carbon coating layer can contribute a considerable specific surface area, and on the other hand, it can also shorten the migration path of lithium ions inside the material.

[0020] 3. Tetrachlorobenzoquinone as a coating layer has high stability. Its π-π conjugated structure can provide additional capacity for lithium-ion batteries. The carbonyl functional groups it contains can react with the amino functional groups in polyaniline, improving the tightness of the connection between materials and further enhancing the electrochemical performance of the battery.

[0021] 3. Through the design of R1≥R2 in the present invention, the core-shell structure is stabilized, which can improve the liquid retention ability of the electrolyte inside the battery and thus enhance the cycling performance and improve the rate performance.

[0022] In summary, through structural design and material optimization, the present invention significantly improves the comprehensive performance of the positive electrode material of lithium-ion batteries, solves multiple deficiencies in the prior art, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in combination with the drawings, where

[0024] Figure 1 is the morphology diagram of the ternary composite positive electrode material proposed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The following further illustrates the present invention in combination with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments cited do not limit the present invention.

[0026] In an embodiment of the present application, a ternary composite cathode material is provided, which has a core-shell structure. The core is a ternary material;

[0027] The surface of the ternary material is porous, and the pores are R1;

[0028] An additive is provided inside the pores;

[0029] The additive is molybdenum trioxide and polyaniline;

[0030] Both the molybdenum trioxide and the polyaniline can be placed inside the pores of the ternary material;

[0031] The particle size of molybdenum trioxide is D1;

[0032] The particle size of the polyaniline is D2;

[0033] The shell is nitrogen-doped porous carbon and tetrachlorobenzoquinone, and the pores of the nitrogen-doped porous carbon are R2;

[0034] Wherein, R1≥D1≥D2≥R2.

[0035] From the above characteristics, the following conclusion can be drawn: The composite cathode material that has completed the "composite" treatment has the following structure:

[0036] Structure: The ternary material has holes on its surface, the pores are R1, there is molybdenum trioxide with a particle size of D1 and polyaniline with a particle size of D2 in the holes; and, there is nitrogen-doped porous carbon and tetrachlorobenzoquinone on the surface of the ternary material, the pores of the nitrogen-doped porous carbon are R2, where R1≥D1≥D2≥R2.

[0037] In summary, the ternary composite cathode material provided in the embodiment of the present application can overcome the deficiencies existing when the ternary material is used alone. By optimizing the material structure, molybdenum trioxide and polyaniline are placed inside the pores of the ternary material, improving the electrical conductivity of the material at room temperature, effectively reducing the internal resistance of the battery. When the operating temperature of the battery reaches the thermosensitive temperature of molybdenum trioxide and above, thermal expansion will occur, forming multiple continuous electron barrier layers, creating an internal block inside the battery to prevent further thermal runaway of the lithium-ion battery and improving the passing rate of the secondary battery in the puncture test, thermal runaway test, drop test, and high-temperature test. At the same time, molybdenum trioxide has high mechanical strength, good stability, and good heat resistance, and can well protect the material in the case of mechanical abuse of the battery (such as puncture and extrusion), further reducing or even avoiding internal short circuit, thereby improving the puncture safety of the battery, enhancing the safety performance of the battery, and also enhancing the high-temperature resistance of the battery, stabilizing the interface, improving the stability of the material, and improving the cycle performance of the battery.

[0038] Meanwhile, nitrogen-doped porous carbon and tetrachlorobenzoquinone are uniformly coated on the surface of the ternary material, which can stabilize the structure of the ternary material, prevent the material from dissolving in the electrolyte and causing the collapse of the ternary material structure, thereby improving the electrochemical cycle of the material.

[0039] Furthermore, the pore size of the ternary material is R1, the particle size of the molybdenum trioxide is D1, the particle size of the polyaniline is D2, and the pore size of the nitrogen-doped porous carbon is R2. The ternary material and the nitrogen-doped porous carbon satisfy the following relationship:

[0040] R1≥D1≥D2≥R2;

[0041] It should be noted that:

[0042] D1≥D2 is to make the polyaniline stack around the molybdenum trioxide, which will form a continuous conductive network and improve the conductivity of the battery. When the operating temperature of the battery reaches the thermosensitive temperature of the molybdenum trioxide and above, thermal expansion will occur, forming multiple continuous electron barrier layers, creating an internal block inside the battery to prevent further thermal runaway of the lithium-ion battery.

[0043] R1≥R2 is to prevent the additives from flowing out of the pores during the battery cycle, which may affect the structure of the ternary material, as well as the cycle stability and specific capacity of the battery.

[0044] Furthermore, the weight ratio of the molybdenum trioxide particles to the polyaniline particles is (30 - 40) to (60 - 70);

[0045] Specifically, it can be: 30:70, 33:67, 35:65, 37:63, 38:62, 40:60, or any other weight ratio.

[0046] Furthermore, the weight ratio of the nitrogen-doped porous carbon to the tetrachlorobenzoquinone is (60 - 70) to (30 - 40);

[0047] Specifically, it can be: 60:40, 62:38, 65:35, 67:33, 68:32, 60:40, or any other weight ratio.

[0048] Furthermore, the particle size D1 of the molybdenum trioxide is 0.2 - 0.8 μm;

[0049] Specifically, it can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or any size within 0.2 - 0.8 μm.

[0050] Furthermore, the particle size D2 of the polyaniline is 0.01 - 0.1 μm;

[0051] Specifically, it can be 0.01μm, 0.02μm, 0.03μm, 0.04μm, 0.05μm, 0.07μm, 0.09μm, 0.1μm or any size ranging from 0.01 - 0.1μm.

[0052] Further, R1 is 0.5 - 1μm and R2 is 5 - 20nm

[0053] Specifically, R1 can be 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, or any size ranging from 0.5 - 1μm;

[0054] R2 is 5nm, 7nm, 10nm, 15nm, 17nm, 20nm, or any size ranging from 5 - 20nm.

[0055] Further, the mass fraction of the additive in the ternary composite cathode material is 1 - 10wt%;

[0056] Specifically, it can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any value ranging from 1 - 10wt%.

[0057] Further, the ternary material is NCM811, NCM622 or NCM523.

[0058] As mentioned above, molybdenum trioxide is used to solve the problem of poor thermal stability of the ternary material. Although the high-nickel ternary material has a high capacity, its thermal stability is poor and it is prone to thermal runaway at high temperatures. By filling molybdenum trioxide in the ternary material, the thermosensitive characteristics of molybdenum trioxide can be utilized to form an electron barrier layer at high temperatures, thereby improving the safety of the battery.

[0059] As mentioned above, polyaniline is a conductive organic substance and is used to solve the problem of poor conductivity of the ternary material. Although the ternary material has a high capacity, its conductivity is poor. By combining the ternary material with a conductive functional material, the high stability, easy processability and conductivity of polyaniline can be utilized to construct a continuous electron network at room temperature, thereby improving the electrochemical performance of the battery.

[0060] The core-shell structure design of the ternary composite cathode material enables polyaniline and molybdenum trioxide to act synergistically, ensuring both the conductive performance of the battery and improving its thermal stability and safety.

[0061] Polyaniline can improve the conductive performance of the material at room temperature, thereby effectively reducing the internal resistance of the battery.

[0062] Molybdenum trioxide will melt when the battery reaches a certain temperature, forming a continuous electron barrier layer, which helps to form a block inside the battery and plays a role in buffering and weakening the short-circuit current.

[0063] When the battery temperature rises, molybdenum trioxide will undergo thermal expansion, forming multiple continuous electron barrier layers, creating an internal block inside the battery to prevent further thermal runaway of the lithium-ion battery.

[0064] In summary, the adoption of polyaniline is to improve the conductivity and safety of the battery. Especially under high-temperature conditions, the response mechanism of molybdenum trioxide prevents battery thermal runaway, thereby enhancing the overall performance and reliability of the battery. Nitrogen-doped porous carbon is used to stabilize the structure of the ternary material, preventing the material from dissolving in the electrolyte and causing the collapse of the ternary material structure, thus improving the electrochemical cycle of the material.

[0065] In addition, an embodiment of the present application also provides a preparation method of the ternary composite cathode material as described above, including:

[0066] Fusing the ternary material, molybdenum trioxide, and polyaniline by a high-speed mechanical fusion method, so that the molybdenum trioxide and polyaniline enter the pores of the ternary material.

[0067] As mentioned above, the high-speed mechanical fusion method is an industrial mixing technique that involves using a high-speed rotating mechanical device to mix different materials. This method is used to prepare composite materials to ensure uniform distribution and good interfacial bonding between the components. Through high-speed mechanical fusion, this method can effectively mix the ternary material, molybdenum trioxide, and polyaniline evenly, ensuring good contact and interfacial bonding between the materials.

[0068] Furthermore, the process of depositing nitrogen-doped porous carbon and p-chloranil on the surface of the ternary material includes: placing the ternary material in a reactor, purging with a protective gas and a reducing gas, loading the powdered nitrogen-doped porous carbon and powdered p-chloranil through a carrier gas, and reacting at 100°C to 200°C for 40 min to 60 min; after the reaction is completed, washing, demagnetizing, and drying are carried out, and then low-temperature calcination is carried out.

[0069] Specifically, the reaction temperature can be 100°C, 150°C, 200°C, etc., and the reaction time can be 40 min, 50 min, 60 min, etc. The protective gas can be but is not limited to nitrogen, and the reducing gas can be but is not limited to hydrogen.

[0070] In the actual operation process, the ternary material can be placed in a fixed-bed reactor, nitrogen can be introduced to expel air, heated to the reaction temperature, and a mixed gas formed by nitrogen and hydrogen is introduced at a rate of 40 mL / min to 60 mL / min for purging. The powdered nitrogen-doped porous carbon and powdered tetrachlorobenzoquinone are loaded by helium, and the reaction proceeds for about 60 minutes. After the reaction is completed, washing is carried out to remove the unreacted impurities on the surface. After demagnetization by a magnetic bar, it is dried under the condition of 95 °C.

[0071] The preparation process of the nitrogen-doped polymeric porous carbon includes: carbonizing a nitrogen-containing high-molecular organic compound in an inert atmosphere to obtain nitrogen-doped porous carbon; the carbonization temperature is 600 °C - 1000 °C, the heating rate is 0.5 °C / min - 5 °C / min, and the carbonization time is 1 h - 48 h.

[0072] Specifically, the nitrogen-containing high-molecular organic compound is one or more of polyaniline, polypyrrole, or polydopamine. The carbonization temperature can be 600 °C, 700 °C, 800 °C, 900 °C, 1000 °C, etc., and the drying time can be 1 h, 2 h, 5 h, 10 h, 20 h, 30 h, 45 h, 48 h, etc.

[0073] In some embodiments, a battery positive electrode plate can be further prepared by using the above ternary composite positive electrode material, and then a secondary battery can be further obtained. By optimizing the positive electrode material, the comprehensive performance of the battery can be significantly improved.

[0074] The embodiment of the present invention also provides a positive electrode plate, which includes a current collector and a positive electrode active layer. The positive electrode active layer is disposed on at least one surface of the current collector. Exemplarily, it can be disposed on two side surfaces of the current collector along the thickness direction. The positive electrode active layer is obtained by coating the current collector with a positive electrode active paste, and the positive electrode active paste includes the above ternary composite positive electrode material.

[0075] Specifically, the selection of the current collector is related to the polarity. The current collector of the positive electrode plate is generally aluminum foil, and the current collector of the negative electrode plate is generally selected as copper foil. Of course, the current collector can also adopt a composite current collector, which will not be elaborated in the embodiments of the present invention. The positive electrode active paste is obtained by dispersing a positive electrode material, a conductive agent, and a binder in a solvent. Exemplarily, the conductive agent can be selected as acetylene black, the binder can be selected as polyvinylidene fluoride (PVDF), and the solvent can be selected as N-methylpyrrolidone (NMP). And further exemplarily, the mass percentages of the ternary composite positive electrode material, the conductive agent, and the binder are (50 - 93%):(1 - 25%):(5 - 25%).

[0076] Embodiments of the present invention also provide a lithium-ion battery. Specifically, the lithium-ion battery includes the above-mentioned positive electrode sheet, and further includes a housing, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet, the separator, and the negative electrode sheet are sequentially placed and formed into an electrode core by winding or laminating, and finally the electrode core is placed in the housing and the electrolyte is injected to obtain the battery. Since the lithium-ion battery includes the above-mentioned positive electrode sheet, the lithium-ion battery also has the advantages of high cycle performance and safety performance.

[0077] Example 1

[0078] The present invention provides a ternary composite positive electrode material with a core-shell structure, which is prepared by the following method:

[0079] S1. A ternary material (NCM811) with a particle size of 15 μm and a pore size of 0.8 μm is mixed with molybdenum trioxide with a particle size of 0.5 μm and polyaniline with a particle size of 0.05 μm in a high-speed mechanical fusion (rotation speed: 4600 revolutions per minute, time: 2 hours) to form the core of the ternary composite positive electrode material, where: the weight ratio of molybdenum trioxide to polyaniline is 30:70, and the mass fraction of molybdenum trioxide and polyaniline in the ternary composite positive electrode material is 1 wt%.

[0080] S2. The core of the ternary composite positive electrode material is placed in a reactor, purged with a mixed gas of nitrogen and hydrogen introduced at 40 mL / min, and powdered nitrogen-doped porous carbon and p-chloranil are introduced by helium. The reaction lasts for about 60 min and is dried at 95 °C to obtain the ternary composite positive electrode material. The thickness of the coating layer is 5 nm, where the pore size of the nitrogen-doped porous carbon is 10 nm, and the weight ratio of the nitrogen-doped porous carbon to the p-chloranil is 60:40.

[0081] The SEM diagram of the obtained ternary composite positive electrode material is as Figure 1 shown. It can be seen from Figure 1 that the coating layer uniformly wraps the surface of the active material.

[0082] Example 2

[0083] This embodiment provides a ternary composite positive electrode material, which is different from Example 1 in that: the mass fraction of molybdenum trioxide and polyaniline in the ternary composite positive electrode material is 5 wt%.

[0084] Example 3

[0085] This embodiment provides a ternary composite positive electrode material, which is different from Example 1 in that: the mass fraction of molybdenum trioxide and polyaniline in the ternary composite positive electrode material is 10 wt%.

[0086] Example 4

[0087] This embodiment provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: a ternary material (NCM811) with a particle size of 15 μm and a pore size of 0.5 μm is combined with molybdenum trioxide with a particle size of 0.3 μm and polyaniline with a particle size of 0.02 μm and mechanically fused at high speed to form the core of the ternary composite cathode material.

[0088] Embodiment 5

[0089] This embodiment provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: a ternary material (NCM811) with a particle size of 15 μm and a pore size of 1 μm is combined with molybdenum trioxide with a particle size of 0.8 μm and polyaniline with a particle size of 0.1 μm and mechanically fused at high speed to form the core of the ternary composite cathode material.

[0090] Embodiment 6

[0091] This embodiment provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: a ternary material (NCM811) with a particle size of 15 μm and a pore size of 1 μm is combined with molybdenum trioxide with a particle size of 0.6 μm and polyaniline with a particle size of 0.05 μm and mechanically fused at high speed to form the core of the ternary composite cathode material.

[0092] Embodiment 7

[0093] This embodiment provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: the chemical formula of the active material is a ternary material (NCM622).

[0094] Comparative Example 1

[0095] This comparative example provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: there is no coating layer on its surface, that is, there is no nitrogen-doped porous carbon and tetrachlorobenzoquinone on the surface.

[0096] Comparative Example 2

[0097] This comparative example provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: it does not contain molybdenum trioxide and polyaniline inside.

[0098] Comparative Example 3

[0099] This comparative example provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: there is no tetrachlorobenzoquinone on its surface, only nitrogen-doped porous carbon.

[0100] Comparative Example 4

[0101] This comparative example provides a ternary composite cathode material, which is different from that of Embodiment 1 in that: the particle sizes of both molybdenum trioxide and polyaniline are 0.8 μm.

[0102] Comparative Example 5

[0103] This comparative example provides a ternary composite cathode material, which is different from that of Example 1 in that the mass fractions of molybdenum trioxide and polyaniline in the ternary composite cathode material are 0.5 wt%.

[0104] Comparative Example 6

[0105] This comparative example provides a ternary composite cathode material, which is different from that of Example 1 in that the pore size of the nitrogen-doped porous carbon is 0.8 μm.

[0106] Comparative Example 7

[0107] This comparative example provides a ternary composite cathode material, which is different from that of Example 1 in that the weight ratio of molybdenum trioxide to polyaniline is 70:30.

[0108] Test Example

[0109] The lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-7 were charged at a constant current of 1C at room temperature of 25°C, with a cut-off current of 0.05C, rested for 10 min, and discharged at 0.7C, and cycled 1000 times in sequence, and the capacity retention rate (%) after 1000 cycles was calculated.

[0110] The lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-7 were formed and subjected to subsequent capacity tests, and the first discharge efficiency of the battery cells was measured. The formula is: first discharge capacity / (formation capacity + first charge capacity).

[0111] The positive electrode conductivities of the positive electrode sheets prepared in Examples 1-7 and Comparative Examples 1-7 were measured under the following test conditions: the conductivity of the surface of the positive electrode material was measured using a Huace high-temperature four-probe tester HEST800 instrument.

[0112] For the nail penetration test, after the single cell was prepared as specified, a high-temperature resistant steel needle with a diameter of Φ5mm - Φ8mm (the conical angle of the needle tip was 45° - 60°, and the surface of the needle was smooth, free of rust, oxide layer and oil stain) was penetrated from the direction perpendicular to the battery plate at a speed of (25 ± 5) mm / s. The penetration position should be close to the geometric center of the nail penetration surface, and the steel needle remained in the battery. The test results are shown in Table 1.

[0113]

[0114]

[0115] Referring to the data in Table 1:

[0116] The batteries prepared in Examples 1-7 have good electrochemical performance and safety performance.

[0117] Compared with Example 1-7, Comparative Example 1 is different in that the nitrogen-doped porous carbon coating layer and chloranil are not provided. As a result, the conductivity performance of the electrode sheet is significantly reduced, and the initial efficiency and cycling performance of the battery become worse. The reasons are as follows: The nitrogen-doped porous carbon itself has good conductivity and is uniformly coated on the surface of the ternary material, which can stabilize the structure of the ternary material and prevent the material from dissolving in the electrolyte, resulting in the collapse of the ternary material structure, thereby improving the electrochemical cycle of the material. The conjugated Π structure of chloranil can provide additional capacity for the battery. The lack of chloranil will reduce the initial efficiency of the battery, and the Π conjugated structure of chloranil cannot form a chemical reaction with polyaniline, thus affecting the electrical cycling performance of the battery.

[0118] Compared with Example 1-7, Comparative Example 2 is different in that molybdenum trioxide and polyaniline are not provided. As a result, the conductivity and safety of the electrode sheet will decrease. The reason is that molybdenum trioxide and polyaniline are placed in the pores of the ternary material, which improves the conductivity of the material at room temperature, can effectively reduce the internal resistance of the battery, thereby improving the cycling performance of the battery. The polyaniline accumulates around the molybdenum trioxide, forming a continuous conductive network, which improves the conductivity of the electrode sheet. At the same time, molybdenum trioxide has high mechanical strength, good stability and good heat resistance, and can well protect the material in the case of mechanical abuse of the battery (such as pinprick and extrusion), further reducing or even avoiding internal short circuit, thereby improving the pinprick safety of the battery and enhancing the safety performance of the battery.

[0119] Compared with Example 1-7, Comparative Example 3 is different in that chloranil is not provided. The conductivity of the electrode sheet and the safety performance of the battery are not much different, but there is a relatively obvious impact on the initial efficiency and electrical cycling performance of the battery.

[0120] Compared with Example 1-7, Comparative Example 4 is different in that the particle sizes of molybdenum trioxide and polyaniline are the same as the pore sizes on the surface of the ternary material. As a result, the polyaniline cannot accumulate around the molybdenum trioxide and cannot form a continuous network structure, thus affecting the conductivity of the electrode sheet and the electrical cycling performance of the battery.

[0121] Compared with Example 1-7, Comparative Example 5 is different in that the mass fractions of molybdenum trioxide and polyaniline are lower than the set values, resulting in a decrease in the electrical cycling performance and safety performance.

[0122] Compared with Example 1-7, Comparative Example 6 is different in that the pore size of the nitrogen-doped porous carbon is 0.8 μm. As a result, molybdenum trioxide and polyaniline are likely to flow out of the pores of the shell, resulting in a decrease in the electrical cycling performance and safety performance.

[0123] Compared with Example 1-7, Comparative Example 7 is different in that the weight ratio of molybdenum trioxide and polyaniline is outside the set range, which affects the electrical cycling performance of the battery.

[0124] Summary: The present invention improves the electrical conductivity of the material at room temperature by placing molybdenum trioxide and polyaniline in the pores of the ternary material, which can effectively reduce the internal resistance of the battery. When the operating temperature of the battery reaches the molybdenum trioxide thermistor temperature and above, thermal expansion will occur to form multiple continuous electronic barrier layers, forming an internal block inside the battery to prevent further thermal runaway of the lithium-ion battery, and improve the pass rate of the secondary battery in puncture tests, thermal runaway tests, drop tests, and high temperature tests. At the same time, molybdenum trioxide has high mechanical strength, good stability, and good heat resistance. It can protect the material well in the case of mechanical abuse of the battery (such as needle puncture, extrusion), further reduce or even avoid the occurrence of internal short circuits, thereby improving the needle puncture safety of the battery, improving the safety performance of the battery, and can also enhance the high temperature resistance of the battery, stabilize the interface, improve the stability of the material, and improve the cycle performance of the battery.

[0125] By setting nitrogen-doped porous carbon and tetrachlorobenzoquinone as coating layers on the surface of the ternary material, a multi-layer dense film is obtained. The nitrogen-doped porous carbon coating layer can contribute a considerable specific surface area on the one hand, and on the other hand, it can also shorten the migration path of lithium ions inside the material. Tetrachlorobenzoquinone as a coating layer has high stability, and its π-π conjugated structure can provide additional capacity for lithium-ion batteries. The carbonyl functional group it contains can react with the functional group amino group in polyaniline, improve the tightness of the connection between materials, and further improve the electrochemical performance of the battery.

[0126] Obviously, the above embodiments are merely examples for the purpose of clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A ternary composite positive electrode material, characterized in that: It is a core-shell structure, the core is a ternary material, the surface of the ternary material is porous, additives are arranged in the pores, the additives are molybdenum trioxide and polyaniline, and the shell is nitrogen-doped porous carbon and tetrachlorobenzoquinone, wherein the pores of the ternary material are R1, the pores of the nitrogen-doped porous carbon are R2, the particle size of the molybdenum trioxide is D1, the particle size of the polyaniline is D2, and R1≥D1≥D2≥R2.

2. The ternary composite cathode material according to claim 1, characterized in that: The weight ratio of the molybdenum trioxide particles to the polyaniline particles is (30-40) to (60-70).

3. The ternary composite cathode material according to claim 1, characterized in that: The weight ratio of the nitrogen-doped porous carbon to the tetrachlorobenzoquinone is (60-70) to (30-40).

4. The ternary composite cathode material according to claim 1, characterized in that: The particle size D1 of the molybdenum trioxide is 0.2-0.8 μm, the particle size D2 of the polyaniline is 0.01-0.1 μm, the R1 is 0.5-1 μm, and the R2 is 5-20 nm.

5. The ternary composite cathode material according to claim 1, characterized in that: The thickness of the shell is 1-10 nm, and the mass fraction of the additives in the ternary composite positive electrode material is 1-10 wt %.

6. The method for preparing the ternary composite cathode material according to any one of claims 1 to 5, comprising: High-speed mechanical fusion of the ternary material, molybdenum trioxide, and polyaniline, so that the additive enters the pores to obtain the core of the ternary composite positive electrode material; Nitrogen-doped porous carbon and tetrachlorobenzoquinone are deposited on the core of the ternary composite positive electrode material, and then low-temperature calcination is performed to obtain the ternary composite positive electrode material.

7. The preparation method according to claim 6, characterized in that: The process of depositing nitrogen-doped porous carbon and tetrachlorobenzoquinone comprises: placing the core of the ternary composite material in a reactor, introducing protective gas and reducing gas for purging, loading powdered nitrogen-doped porous carbon and powdered tetrachlorobenzoquinone through carrier gas, and reacting at 100° C. to 200° C. for 40 min to 60 min.

8. The preparation method according to claim 7, characterized in that: The preparation process of nitrogen-doped porous carbon includes: carbonizing nitrogen-containing high molecular organic matter under an inert atmosphere; the carbonization temperature is 600°C-1000°C, the heating rate is 0.5°C / min-5°C / min, and the carbonization time is 1h-48h.

9. A pole piece, characterized in that: A ternary composite positive electrode material comprising the ternary composite positive electrode material described in any one of claims 1 to 5 or a ternary composite positive electrode material obtained by the preparation method of the ternary composite positive electrode material described in any one of claims 6 to 8.

10. A battery, characterized in that: Including the pole piece as claimed in claim 9.

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